THE EVIDENCE. 69 



these forms, to begin with, is generally extremely difficult, for 

 it is often associated with other forms, most of which have no 

 disease-producing power, and the experimenter generally has 

 no guide as to which is the one wanted until he has carried 

 it through the cultivations and has made some inoculations. 

 In many of the diseases he is met with another difficulty, 

 which he often has no guide whatever in surmounting, in the 

 fact that he does not know what animals are susceptible to the 

 disease. A considerable number of diseases in men have not 

 been known among animals, and under existing notions he 

 cannot experiment upon men. And then the work is 

 necessarily very slow. The thought of the present time de- 

 mands absolute demonstration. No possible error is admis- 

 sible. Dr. Koch spent two years in cultivating the bacillus 

 tuberculosis and making inoculations with it, before he was 

 satisfied to announce it. He induced the disease by inocula- 

 tion with this bacillus in over one hundred different animals, 

 watched most of them until death from the disease induced, 

 and examined them macroscopically and microscopically, to 

 be absolutely sure there was no mistake. This is what the 

 scientific world will demand in case of each and every disease. 

 The work will be very slow, and years will be required for its 

 accomplishment. 



THE EVIDENCE. 



The evidence that disease-producing bacteria are distinct 

 from the bacteria of the decompositions is now becoming very 

 clear. All the decompositions swarm with bacteria of various 

 kinds, that are entirely free from any causative relation to 

 disease, and evidently, may be tolerated in food or in contact 

 with the mucous membranes, and even in wounds, without 

 any injury whatever. Every one who eats butter which has 

 become even a little strong, consumes a great number of 

 organisms, and yet without the least injury. The same is true 



