ETIOLOGY. 21 



ferred by Bollinger that the bacilli produce the diseased condition 

 by accumulating in large numbers in these important organs, and 

 mechanically interrupting their functions. This is known as the 

 mechanical interference theory. 



If anthrax were the only infectious disease, or if in other infec- 

 tions the germs were as numerous in the blood as they are in anthrax, 

 the mechanical interference theory would still have strong support, 

 but to the majority of germ diseases it is not at all applicable. 



3. Another answer given to this question, " How do germs cause 

 disease?" is that they do so by consuming the proteids of the body, 

 and thus depriving it of its sustenance. The proteids are known to 

 be necessary for the building up of cells and it is also known that 

 microorganisms feed upon proteids. However, this theory is unten- 

 able for several reasons : in the first place, many of the infectious dis- 

 eases destroy life so quickly that the fatal effects cannot be supposed 

 to be due to the consumption of any large amount of proteid ; in the 

 second place, the distribution of the microorganisms is such that 

 they do not come in contact with any large proportion of the pro- 

 teids of the body ; in the third place, the symptoms of the majority 

 of the bacterial diseases are not those which would be produced by 

 withdrawing from the various organs their food. The symptoms are 

 not those of starvation. 



4. Still another theory, which has been offered, is that the 

 bacteria destroy the blood corpuscles, or lead to their rapid dis- 

 integration. But in many of the infectious diseases, as has 

 been stated,the microorganisms, although abundant in some or- 

 gans, are not present in the blood. Moreover, the disintegration 

 of the blood corpuscles is not confirmed by microscopical exami- 

 nation. 



5. Seeing the vital deficiencies in the above theories, and being 

 impressed by the results obtained by the chemical study of putrefac- 

 tion, bacteriologists have been led to inquire into the possibility 

 of the symptoms of the infectious diseases being due to chemical 

 poisons. In investigating this theory, the following possibilities 

 suggest themselves : 



(a) The microorganisms may be intimately associated with, or 

 may produce, a soluble chemical ferment, which by its action on the 

 body produces the symptoms of the disease and death. At one time 

 this theory had a number of ardent supporters, among whom might 

 be mentioned the eminent scientist De Bary ; but Pasteur proved 

 the theory false when he filtered anthrax blood through earthen 

 cylinders, inoculated animals with the filtrate and failed to pro- 

 duce any effect. Nencki made a similar demonstration when he 

 inoculated a two per cent, gelatin preparation with the anthrax 

 bacillus, which liquefied the gelatin, and on standing the bacilli 

 settled to the bottom, after which the supernatant fluid which was. 



