RELATION TO INFECTIOUS DISEASES. 95 



dis3ase is chemical in character, it becomes evident that no 

 one is justified in saying that one germ is the sole source of 

 that poison. Such a statement would be as unwarranted 

 as one that the coffee tree is the sole source of caffein, or 

 that the strychnos Ignatii is the only species of the nat- 

 ural order Loganiacese which produces a convulsive poison. 

 In other words, the specific cause of a given disease is not 

 to be determined AvhoUy by the morphology of the germ, 

 but by the character of the chemical poison which is the true 

 materies morbi. 



Bacteria cannot be classified, so fiir as their causal rela- 

 tionship to disease is concerned (and this is the most im- 

 portant knowledge to be gained from them), until we know 

 tlie nature of their chemical products, for it is by virtue of 

 these that the germs have any causal relationship to dis- 

 ease. 



It is possible that two germs may be unlike in form, and 

 yet they may produce poisons which are identical or those 

 which are very similar in their effects upon man. One 

 germ may be stained by Gram's method and another fail 

 to be acted upon when so treated ; but this does not prove 

 that their chemical products are totally unlike. This is 

 not only a possibility, it is a fact which has been demon- 

 strated repeatedly, both with pathogenic and non-pathogenic 

 organisms. A few illustrations may be given here : The 

 yeast plant is not the only microorganism which will pro- 

 duce alcohol in saccharine solutions. The same product 

 results from the growth of the bacterium Bischleri, bac- 

 terium coli commune, bacterium ilei, bacterium ovale ilei, 

 bacterium lactis aerogenes, and others (Nencki). Mor- 

 phologically, there are marked differences between the yeast 

 plant and these bacteria, but they alike produce alcohol. 

 More than a dozen germs, including both micrococci and 

 bacilli, are capable of generating lactic acid. Some of these 

 produce an acid which is optically inactive ; others, one 

 which is dextro-rotatory; and others still, one which is Isbvo- 

 rotatory. The tetanus germ of Kitasato and that of 

 TizzONi and Cantani arc known to be different. Cultures 

 of the former in bouillon are virulent, while those of the 



