22 THE ETIOLOGY OF THE BACTERIAL DISEASES. 



clear and alkaline in reaction, was filtered and injected into animals 

 without producing any effect. 



It must not be inferred from the above statements that bacteria 

 do not produce ferments. Many of them do form both diastatic and 

 peptic ferments, which may retain their activity after the bacteria 

 have been destroyed ; but there is no proof in any case that these 

 ferments have a causal relation to the disease. After the disease 

 process has been inaugurated some of these ferments probably play 

 an important part in the production of morphological changes, the 

 nature of which will be indicated when the different diseases are dis- 

 cussed. 



(6) The microorganisms may act either directly or indirectly as 

 ferments, splitting up complex proteids in the tissue and producing 

 among these split products the specific poisons which induce the 

 characteristic symptoms of the disease, and may cause death. This 

 theory, once quite generally held, has stimulated numerous investi- 

 gations, some of which have led to important discoveries ; but at 

 present it is safe to say that among the bacterial split products formed 

 either in artificial culture media or in the body, there is not found 

 one which, on account of its intensity of action or from the nature of 

 the symptoms which it produces, can be regarded as the specific cause 

 of any one of the infectious diseases. Moreover, it has been shown 

 that some of the most virulent germs, as for instance, the bacillus of 

 tetanus, will grow and retain their virulence in artificial cultures 

 made up principally of inorganic substances and containing only 

 minute quantities of organic bodies of such simple construction that 

 it must be admitted that the specific toxins of these microorganisms 

 cannot result from their cleavage action. 



While we are forced to conclude that no specific toxin has been 

 found among the cleavage products of bacteria, it is well established 

 that certain powerful poisons originate in this way, and it will come 

 within the scope of this treatise to deal with all substances formed by 

 the cleavage action of bacteria, both upon the constituents of artificial 

 culture media and within the animal body. 



(o) Poisons may be produced by the cellular activity of bacteria 

 much in the same way as morphin is formed in the poppy. This 

 theory supposes that the formation of bacterial toxins is a synthetical, 

 rather than an analytical, process. It is now generally believed that 

 most, if not all, of the pathogenic microorganisms consist of cell walls 

 containing cell protoplasm, and that the specific toxin is a constit- 

 uent of the protoplasm, and that its formation is one of the vital 

 phenomena manifested by the organism in its processes of growth 

 and multiplication. In some species the cell wall is not easily per- 

 meable and the toxin is found only within the cell ; while in other 

 species the toxin formed within the cell readily passes through the 

 wall and diffuses through the culture media in artificial growths, or 



