LOGIC AND THE SCIENTIFIC METHOD. VIRUS AND TOBACCO MOSAIC DISEASE ‒ WHAT WE KNOW ABOUT INFECTIOUS AGENTS

: In this paper, using the example of the discovery of viruses from the history of science in the experiments of D. J. Ivanovsky, the authors investigate how scientific research functions and how the scientific conception that could be determined as the ruling paradigm is gradually transformed. Respecting logical and scientific-methodological principles, Ivanovsky’s discoveries, in the long run, led to the discovery of viruses as completely new agents and thus to the reconstruction of the paradigm of bacteria as the smallest living disease-causing agents. Thus, he contributed to what is defined as scientific growth in the philosophy of science. Through a comparative analysis, using the example of protective masks, we will show that today there is a tendency that the basic postulates of scientific work, which imply critical examination and the possibility of refutation, are no longer sufficiently respected.


(Translation In Extenso)
Abstract: In this paper, using the example of the discovery of viruses from the history of science in the experiments of D. J. Ivanovsky, the authors investigate how scientific research functions and how the scientific conception that could be determined as the ruling paradigm is gradually transformed. Respecting logical and scientific-methodological principles, Ivanovsky's discoveries, in the long run, led to the discovery of viruses as completely new agents and thus to the reconstruction of the paradigm of bacteria as the smallest living disease-causing agents. Thus, he contributed to what is defined as scientific growth in the philosophy of science. Through a comparative analysis, using the example of protective masks, we will show that today there is a tendency that the basic postulates of scientific work, which imply critical examination and the possibility of refutation, are no longer sufficiently respected.

INTRODUCTION
No definition so far has adequately determined what viruses are. Following Lwoff (André Michel Lwoff), virologists usually say that "a virus is a virus", 3 which does not really have a scientific meaning. On the one hand, viruses may be treated like life form because they are able to multiply, to transfer genetic information and to evolve. However, on the other hand, viruses are inanimate because they do not have a complete and independent cell structure that is in the basis of everything we call living beings or organisms. In addition, viruses have the ability to crystallize, unlike cell organisms (living individuals).
Unlike viruses, in their unicellular structure, bacteria have a complete system that is necessary for replication, and the largest number of them can reproduce independently, outside other living cell systems, which is also a characteristic of other, more complex infectious agents (fungi and parasites).
However, until the end of the 19 th century it was believed that bacteria were the smallest living entities that caused different diseases. 4 It was the prevailing scientific paradigm in that field, while Louis Pasteur was one of its leading proponents. In that respect, he wrote: "You can speak, if you wish, of poisoning. Make that hypothesis, I will accept it. I do not know the mechanism of death from any disease more than you or anyone else, not more than we know about the mechanism of life. Speak of the poison, if you wish, but you will be forced to add that, if a poison causes death, it is the microbe that produces the poison" (Pasteur, 1880, according to: Cavaillon, 2022. A paradigm is a very complex concept introduced in the philosophy of science by Thomas Kuhn and, apart from its philosophical-scientific aspect, it also has its sociological and psychological aspects. It constitutes the prevalent scientific theory (or a set of theories), as well as the metaphysical concept enabling scientists to have "model-problems" and "solutions". This theory lies in the basis of the generally accepted attitudes of the scientific community in a certain period of time that find their articulation mainly in the (high education) textbooks and research publications. As such, it is de facto intangible until a new and bold theory emerges that would, according to Kuhn, represent the reconstruction of the old theory or its refutation due to new findings: "Its adoption demands the reconstruction of the previous theory, as well as the assessment of the previous facts, which is essentially a revolutionary process that can rarely be conducted by an individual, and definitely never overnight" (Kuhn, 1984, p. 47).
In this paper we will apply the historical approach and comparative analysis to attempt, using the example of the virus discovery, primarily the experiments conducted by Dmitri Josifovich Ivanovsky at the end of the 19 th century, to show how rationally founded scientific research functions and how a gradual transformation occurs of a concept that might be determined as the prevailing paradigm. On the other hand, we will show that nowadays 3 It could be said that Lwoff deduced this indefinite tautological definition based on his virus characterization that contained dour basic properties: a virus consists of only one type of nucleic acid (RNA or DNA); it is multiplied with the aid of nucleic acid; those are intracellular obligate parasites; they are made of proteins and nucleic acid (see Marković et al., 1995, pp. 2-3). 4 Today it is a known fact that there are disease-causing agents smaller than viruses: viroids (virus nucleic acids) and prions (virus protein structures).
there is an increasing tendency of introducing psychologisms in science, which affects the basis of hypotheses. As it is well known, Kant was the one who wrote that "everything that in such respect only resembles a hypothesis [is] forbidden goods that must not be offered at the lowest price" (Kant, 1998, p. 10). Critical reconsideration ceases to be desirable, while the principles of logic and scientific methodology are somewhat put aside. Thus, science turns, to a certain extent, into scholastic dogmatics -exactly what it has always criticized. We will also examine how those tendencies are articulated on the example of protective masks, from which the sociological component can also be seen of this epidemiological measure introduced by the governments worldwide within the declaration of the SARS-CoV 2 pandemic.

How viruses and viral diseases were discovered
Initially, virus diseases whose causing agents were invisible under the optical microscopes of the time were ascribed by the scientists to the action of bacterial poisons (Ivanovsky, 1892). 5 Much later, with the discovery of the electronic microscope, viruses became "visible". Modern biology enabled a detailed study of viruses (in the artificial systems of live cells) and it was clearly determined that, if they were able to replicate, they would be added to the group of infectious agents studied by microbiology. 6 Once it enters the sensitive and permissive cell (the cell that suits a certain virus), it will use all the host's potentially infected cells to replicate (i.e., it becomes alive).
For an infectious disease caused by a virus, bacterium, fungus or parasite to develop, it is most frequently necessary that these infectious agents are replicated in the body, i.e., that their number is increased to such an extent that they overpower the defence mechanisms of the immune system and damage the organism by its products (enzymes, toxins) or they force the host's immune system to act self-destructively on the host's own organism.
That is why the basic strategy of treating infectious diseases nowadays is based either on the application of anti-infectious agents that should reduce their number, but without damaging the human body, or on the application of immunomodulatory medications that should reduce the self-destructive immune response. Since, unlike bacteria, fungi and parasites, viruses do not have their metabolism and since they are quite protected within the cell of the infected organism, antiviral medications often have great difficulty in leading to the reduced number of viruses without damaging the host's cells at the same time (see Terzin, 1955, p. 14).

Do we know the origin of viruses -science in the past and today?
Although molecular biology and related sciences have significantly progressed in the last century regarding the discovery of the structure and function of virus genes, science 5 Ivanovsky used the term бактериальный яд. 6 It is important to emphasize that microbiology is closely related to epidemiology when it comes to the identification of disease-causing agents, i.e., the role of microbiology is crucial in the verification of an epidemiological hypothesis (Terzin, 1955). still knows little about the origin and true nature of viruses, whereas much of what science believed to know has turned out to have large limitations. We were assured of it by SARS-CoV (1) from 2003, and even more by the ongoing SARS-CoV (2) from 2019. According to Chinese researchers in the paper published in 2020, SARS-CoV (1) "is probably (emphasized by A. L.) transmitted by bats and civets as intermediary hosts and eventually onto the man" (Chang et al., 2020). The same research has a similar claim regarding the SARS-CoV (2) virus, which was established to be 96% similar to the bat marked as RaTG13, while "the indirect host is not clear", but it is also presumed (emphasized by A. L.) that it is the Asian scaly anteater pangolin (Chang et al., 2020).

Tobacco mosaic disease -a bacterial toxin or a virus
The virus discovery goes back to 1892, when Russian scientist D. J. Ivanovsky published the paper entitled "On two tobacco diseases" in the journal Agriculture and Forestry of the Russian Free Economic Society. The article was the result of his two-year research at the tobacco plantations of the Imperial Nikita Garden in Crimea in 1890 and in the botanical laboratory of the Imperial Academy of Sciences in 1891. At that time, tobacco production was an important agricultural branch, and these diseases caused great damage, so that Ivanovsky's scientific work was initiated primarily by economic interests. On the other hand, however, this paper is also important because of the principles of logic and scientific methodology, and that is why we will further analyze it in detail.
Tobacco being infected was a simple fact, but it was related to economic losses and thus constituted a serious problem that had to be resolved. Scientific work was supposed to establish a connection between the disease and its causing agent. That is why Ivanovsky proposed and examined several potential hypotheses he believed to be in the basis of this disease, thinking that by confirming at least one of the hypotheses he would resolve the problem of mosaic tobacco disease.
First, he refuted the hypotheses referring to fungi or some previously unknown smaller bacteria, and then went on to examine the hypothesis about a bacterial poison as the most probable cause of this disease. At that time, his hypothesis was rather bold having in mind the consequence it caused d in the further development of science. Namely, he undermined the former generally accepted paradigm about bacteria as the smallest living disease-causing agents and paved the way for the research that in mid-1939 led to seeing the virus with the aid of the electronic microscope. 7 It was a laborious scientific road because the greatest scientists of the time were staunch proponents of the thesis about bacteria as the smallest infectious agents. Despite Ivanovsky's great effort and experimental work in isolating the cause of the disease producing the poisonous excretion, (he believed it was an unknown bacterium), he failed. The hypothesis was wrong. Nevertheless, his research procedure referring to the refutation or acceptance of some hypotheses lies in the foundation of the scientific explanation of reality, showing that even "wrong hypotheses" can be useful. 7 The first images of the tobacco mosaic virus by the electronic microscope were made in 1939 by Gustav Kausche, Edgar Pfankuch and Helmut Ruska (see Kausche et al., 1939).
In his work, Ivanovsky criticized Mayer's (Adolf Eduard Mayer) opinion in relation to mosaic tobacco disease. Namely, he believed that the disease had two stages, while Ivanovsky experimentally/ showed that those were actually two separate diseases -pox disease (Рябуха in Russian, Pockenkrankheit in German) and marble disease. For the latter, he accepted the name "mosaic disease", agreeing about it with Mayer, who gave the disease this name within his research in 1886 in the Netherlands: "Having this in mind, I kept Mayer's name "mosaic disease" for marble disease, although I understand this name only as part of what is implied by Mayer" (Ivanovsky, 1892, p. 9). However, he did not agree with Mayer that a bacterium is the cause of mosaic tobacco disease: "On the other hand, the author's belief, as it has already been said, does not completely agree with his opinion that mosaic tobacco disease comes from a bacterial infection" (Ivanovsky, 1892, p. 19).

How Ivanovsky tested the hypothesis about bacteria and mosaic disease
Ivanovsky reached the conclusion that bacteria did not cause mosaic tobacco disease on the basis of the following empirical facts: -the agent is not visible under the microscope (unlike bacteria); -the agent passes through Chamberland's porcelain filter (while bacteria do not); -the agent does not grow on nutrient media 8 (while bacteria do); From the above-mentioned we can see that Chamberland's filter had an extremely important role. Charles Chamberland made this filter in cooperation with Louis Pasteur in 1884. Its smallest pores had the size of 0.1 µм and could not filter bacteria and other cells (bacteria size is 1-10 µм or more). That is why it was believed that the liquid going through this filter was bacteriologically sterile. However, viruses are several dozen times smaller than average bacteria. The size of the influenza virus is about 0.1 µм (Terzin, 1955) and that is why viruses pass through the pores of this filter, which Ivanovsky proved experimentally. The liquid squeezed from the infected tobacco leaves, when passing through Chamberland's filter, was still infectious: "According to my experiments, the extract completely cleaned by such filtration, obtained from tobacco leaves infected by mosaic disease, will cause the disease just like the extract that has not been filtered" (Ivanovsky, 1892, p. 19). 9 In a logical and methodologically proper manner he reached the conclusion that it was something else, but still of bacterial nature, and he named the so-called filterable pathogen 8 These are artificial inanimate nutrient media for isolating bacteria, used by Ivanovsky in his experiment. In that respect, he says the following: "Therefore, what remains is to isolate the microorganism that causes the disease. For that purpose, I infected with the juice of the affected plants different artificial nutrient mixtures: boiled potatoes, meat-peptone-gelatine, meat-peptone-agar, stock, tobacco decoction with 1% peptone (mildly acid and average), the same decoction with 5% gelatine and, in the end, tobacco-peptone-gelatine (i.e., the decoction of fresh tobacco leaves with 1% peptone and 10% gelatine). All these experiments, demanding plenty of time and effort, had a negative result; the microorganism is obviously unable to grow on these artificial substrates. Mayer's attempts had the same result when he tried to cultivate microorganisms by Koch's apparatus" (Ivanovsky, 1892, p. 21). On the other hand, however, it should be emphasized that viruses can be isolated through the living cell system. a "bacterial poison" (бактериальный яд). In it, he also cited some insights by Émile Roux about microbes acting through their specific poisonous excretions. 10 Roux believed that every infection was actually a case of poisoning: "An infectious disease is actually a case of the organism's poisoning, while the difference is that in this case a poison is not taken from outside, but it is produced inside the organism itself by the bacteria penetrating into it" (Roux, 1891, according to : Ivanovsky, 1892, p. 16).
The hypothesis about bacterial poisons as disease-causing agents was advocated by other scientists as well. As early as 1856. Peter Ludvig Panum wrote about bacterial toxins, while in the 1868 experiment Ernst von Bergmann and Oswald Schmiedeberg managed to isolate a microbial poison which they called a sepsis sulphate. In 1892, Nikolaï Gamaleïa published a book in French entitled Les Poisons Bactériens ("Bacterial Poisons"), in which he claimed that a new science was being developed -bacterial toxicology: "From this set of facts, a new science was born, the science about microbe poisons, which at the same time connects bacteriology, biological chemistry and general physiology" (Gamaleïa, 1892, p. 3).
Therefore, Ivanovsky found out that in mosaic tobacco disease there was most probably a microbial poison or some previously unknown bacterium (of smaller size), and that is why it could pass through Chamberland's filter. That is why the next task he assigned to himself was to isolate the microbe itself. For that purpose, he conducted numerous experiments with growth on various types of nutrient media, but he failed in it.
Six years later, in 1898, Dutch scientist Martinus Willem Beijerinck also proposed a hypothesis that mosaic tobacco disease was not caused by microbes. He described the filterable pathogen as contagium vivum fluidum -a living liquid infectious agent.
He was the first to use the term "virus" for the agents that could be filtered and proposed the key hypothesis that "an infection, in order to reproduce, must be built into the living cell cytoplasm in whose replication is, so to say, passively involved" (Horzinek, 1997, p. 19). Ivanovsky, unfortunately, did not agree with that attitude and even thought that such a hypothesis constituted a sad chapter in the development of science.

Scientific methodology and logic: experiment and deduction
Deduction is a logic procedure in which a conclusion inevitably follows from the premises and has an important role. Searching for a scientific explanation for mosaic tobacco disease, Ivanovsky looked for a universal connection between facts of different types. How did he do it? In his refutation of the hypothesis about bacteria as direct disease-causing agents, he deductively elaborated his experiments. The hypothesis about bacteria could not pass that test. For the sake of reminding the readers, the agent he examined could not be seen under the microscope; it passed through the filter and did not reproduce on the nutrient medium. The methodology and scientific considerations were logically correct. The arguments used by Ivanovsky to refute the first theory can be presented with the aid of Aristotelian syllogisms. (A syllogism is a form of deductive concluding that consists of two 10 Roux presented these insights at the International Congress of Hygiene and Demography in London in 1891. premises and conclusions. As a rule, it has solely three different concepts. The conclusion necessarily derives from the premises.) We will show some forms of syllogisms with the aid of which it is possible to explain how Ivanovsky proved/refuted the hypotheses about bacteria: All bacteria can be seen under the microscope. This agent is not a bacterium. The same arguments may be posed through a deductive conclusion modus tollens, in which the negation of the consequence in the second premise also negates the established condition in the conclusion: If the agent is a bacterium, it is seen under the microscope. This agent is not seen under the microscope. This agent is not a bacterium.
If the agent is a bacterium, it does not pass through Chamberland's filter.

This agent passes through Chamberland's filter.
This agent is not a bacterium.
If the agent is a bacterium, it grows on nutrient media. This agent does not grow on nutrient media. This agent is not a bacterium. In all these cases, either when the first premise claims a universal judgment "All Ss are Ps" (S is the subject and P is the predicate) or poses implications (А→В), the facts obtained from the experiment indicate that this agent could not be a bacterium. A solution might be found by refuting the first premise claiming that there are some smaller bacteria than the previously known bacteria, which are therefore not visible under the microscope and pass through the filter. However, the thesis about smaller bacteria is problematic because it could imply that those miniature bacteria do not act like other bacteria on the nutrient medium, which would disturb the basic rule of the living world. Therefore, Ivanovsky refutes the thesis about bacteria and accepts the coherent thesis about (inanimate) bacterial poison as an excretion that passes through the filter that cannot be seen under the microscope and does not grow on the nutrient medium. Yet, what remains on the filter and exists in the tobacco leaves juice before filtering should contain the said bacteria producing that poison, and, as we have already mentioned, Ivanovsky did not succeed in discovering (isolating) them. That is why a logical solution to the problem remained -that those were poisons without the determinant of "bacterial", i.e., viruses, which was later concluded by Beijerinck.

Chamberland's filter and the role of the mask during the SARS COV 2 pandemic
Chamberland's filter and protective masks, as a filtering protective means during the pandemic, can be compared by citing the experiments conducted by Ivanovsky. The protective measure wearing a mask (of any kind, from those of N95 type to the homemade cotton ones) and Chamberland's filter should act by the same principle and have the same function, meaning that their pores must be impermeable to infectious agents. The example of the virus causing mosaic tobacco disease served to show that the infectious agents passed through Chamberland's filter because it was smaller than the pores of this filter. This principle does not seem to refer to the masks recommended to be worn during the pandemic.
On the website of the Institute of Molecular Genetics and Genetic Engineering of the University of Belgrade, the following is said to be important for understanding the efficiency of protective masks: -the size of the SARS CоV 2 virus is between 0.12 µм and 0.16 µм; -masks with the label N95 block 95% particles of the size 0.3 µм; -surgical masks, if worn by an infected person, reduce the probability of that person infecting other people in his/her surroundings (Institute of Molecular Genetics and Genetic Engineering [IMGGE], 2020). The pore size on N95 masks is 0.15-0.5 µм, while the pore size on surgical masks is about 1 µм. It is impossible to determine the pore size on cotton (homemade) masks because it depends on the texture of the cloth they are made of, but it can be assumed that their size is not smaller than the pores on surgical masks.
Based on the given parameters, it is evident that the pores on all these masks, even those of N95 type, are bigger than the virus whose penetration they should block. If logical concluding, scientific methodology and the experimental example with Chamberland's filter are applied, it follows that these masks cannot block the penetration of the virus into the man's respiratory tract.
The argumentation would be as follows: Everything that is smaller than the pores of protective masks will go through them. All viruses are smaller than the pores of protective masks. All viruses pass through protective masks. The first premise in this argument is the proposition from which we start. The second premise is the factual state, while the conclusion inevitably follows from them. Therefore, the truthfulness of the conclusion depends on the validity of the implication: If the agent is smaller than the filter pores, then it will pass through the filter. Moreover, protective masks are also filters and they have pores of a certain size, which are of a larger diameter than that of the virus, and provided that the given implication is valid, these masks cannot be impermeable to viruses. This particularly refers to surgical and cloth masks.
In the scientific community, there is no general agreement about this matter. In that respect, difference should be made between science and profession. Profession constitutes a set of certain knowledge and skills that may be acquired on the basis of different textbooks and required literature in evening courses, at schools and the university. Professionals (bakers, doctors or pharmacists) strive to finish a job -based on the established and verified protocols, to make or repair something, to cure someone, to make something more beautiful etc. To that end, profession depends on the prevailing scientific paradigm. On the other hand, science primarily implies researching and understanding the world, while respecting logic and special scientific methodology, with the aim of discovering new regularities in nature and society, which will be applied in certain professions. That is why answers about new, so far unknown diseases, should be searched from scientists and not professionals. In that respect, we will list several scientific papers.
In their research, Yuxin Wang et al. have obtained results that speak in favour of the use of any masks as a protective means: "By wearing a mask, even the cloth one, a healthy person's likelihood of being infected is largely reduced in this high-risk environment" (Wang et al., 2021). However, the authors also point out that there are "rather different and controversial opinions about the matter of mask wearing, which led to confusion in the public" (Wang et al., 2021). Yafang Cheng et al. believe that masks are a good preventive measure, especially in combination with airing and social distancing, but they also emphasize that the efficiency of masks is still being seriously discussed by scientists (Cheng et al., 2021).
In contrast, C. Raina MacIntyre et al. have reached a conclusion that masks are not an efficient protective means. "The rate of virus isolation in the control group that did not wear a mask in the first Chinese randomized clinical study was 3.1%, which does not significantly differ from the rate of virus isolation in groups wearing medical masks in any of the three research studies" (see MacIntyre et al., 2015, p. 6). As for cloth masks, they even proved to be harmful in the same study: "Cloth masks led to substantially higher infection rates than the medical masks, and they also had a worse performance than the control group" (see MacIntyre et al., 2015, p. 1). The control group did not have to wear any masks, but behaved in an ordinary way.
In their research, Ignazio Maria Viola et al. emphasize that surgical and cloth masks, as well as face shields, cause the formation of strong jets, due to which virus-filled particles may be dispersed several metres away. That is why the false feeling of safety should be avoided that often appears in persons using these protective means (Viola et al., 2021).
David Carrington from the University of London, in his statement for BBC, says that surgical masks are not efficient protection against air-borne viruses and bacteria because they are mostly not strong enough, they have no air filters, while leaving the eyes exposed to the action of the virus (see BBC NEWS in Serbian, 2020).

Symbolism of mask wearing
The answer to the question why, despite controversies and disagreement of the scientific community, it was insisted to that degree on mask wearing, can be found in psychological factors. Namely, in the "instruction for the use of protective cotton masks, medical and filtering masks", published by the Institute of Public Health of Serbia "Dr Milan Jovanović Batut", 11 there is a particularly outstanding role of cotton masks -"a mask raises awareness of the need for physical distancing of minimum two metres" (Institute of Public Health of Serbia "Dr Milan Jovanović Batut", 2020, Table 1). Such effect on the people's consciousness could be interpreted as a psychological and paternalistic moment that, as a rule, should not be included in a medical (scientifically based) instruction. Kant was also one of those who wrote against psychologisms in science: "If we took principles from psychology, i.e., from the observance about our sense, then we would see only how an opinion develops and what it is like with all kinds of subjective obstacles and conditions; therefore, it would lead to findings of only random laws" (Kant, 2012, pp. 10-11).
Nevertheless, the degree of importance of such psychological factor was shown several decades ago in the film Variola vera directed by Goran Marković. When a doctor in the hospital with the quarantine regime asked the other doctor who had been "sent from the Headquarters" why he was wearing a protective suit when he did not need it, he answered that he did it for psychological reasons. 12 The importance of the psychological moment is also spoken about by Klaus Schwab and Thierry Malleret in their book The great Reset. They remind that the very word "quarantine", dating back to the Middle Ages and deriving from the word quaranta (40 in Italian), since the isolation of the infected usually lasted 40 days. However, as these authors stress: "The 40-day period did not have a medical foundation; it was chosen because of symbolic and religious reasons. Both the Old and the New Testament often refer to number 40 in the context of purification" (Malleret & Schwab, 2020, p. 9).
Therefore, it seems that mask wearing and seeing other people with masks have a particularly great psychological and symbolic function, contained in the fact that it should always be visible that the "invisible enemy" is somewhere out there, i.e., that the invisible should become visible in a specific manner. That is why one of the main roles of mask wearing is to mark every person as a potentially dangerous infection carrier from whom we should keep social distance. In sociological terms, such distance is an abstract concept, but, according to U. Šuvaković, "there, the subject always implies social relationships" (Šuvaković, 2020, p. 451). Whether masks have an adequate role in the protection against viruses is an important question, but what is even more important is that they have an efficient psychological and sociological function. That is why all masks were "welcome", even the cotton ones that are not a medical product, have not been tested and had no certificate about protection against infectious agents (see Table 3).
The history of science, as well as current events, tell us that Russell was right when he said that even when all experts agree about something, they could very easily be wrong (Russell, 2004, p. 2).