226 TEXT-BOOK OF BACTERIOLOGY. 



animals, it may readily be understood that for many years efforts 

 have been made to discover its cause and the mode of its diffusion. 



This seemed to be a hopeless task as long- as science was not 

 united on the preliminary question as to what should be considered 

 tuberculosis, what its limits were, and what were the surest methods 

 for its recognition. 



While some endeavored to form a picture of their judgment 

 from the symptoms of the disease by purely clinical criteria, others 

 looked for a picture of the disease in the tissue changes solely. 



But even in this narrower sphere there was no agreement 

 Laennec, the great French investigator, saw in caseation the real 

 character of the disease. Virchow, on the contra^, recognized 

 as tuberculous only those changes in which there were present the 

 tubercle nodule, those small, millet-seed growths of gray trans- 

 parency which were first described by von Bayle in 1810 as being- 

 peculiar to consumption. 



Villemin, in his observations published in 1865, was the first to 

 open the way out of this controversy. He succeeded by inoculation 

 with tuberculous matter in producing- tuberculosis in previouly 

 healthy animals, and thereby demonstrated that* tuberculosis was 

 an infectious disease. It was Cohnheim above all to whose keen 

 and experienced eye the significance of these facts was apparent, 

 and who, after his own inoculations into the interior chamber of 

 the eye, repeatedly and emphatically declared that it was a specific 

 infectious disease. 



Before his untimely death he saw the correctness of his declara- 

 tions conclusively shown. 



On the 24th of March, 1882, R. Koch, before the Physiological 

 Society in Berlin, made the announcement that he had found the 

 cause of tuberculosis, which was due to a peculiar bacillus of a 

 special shape. 



" I have seldom in all my life felt greater pleasure than at the 

 reception of this news," were the words with w r hich Cohnheim 

 greeted the new discovery, and one could see that he spoke those 

 words with the deepest conviction. 



The impression which the discovery of Koch made was in fact 

 extremely deep and lasting. The incomparable certainty and posi- 

 tiveness of his investigations were admired by everybody. 



In a methodical and conscientious investigation he had paved 

 the way step by step to this knowledge, established his views, and 

 with one stroke disclosed the faultless and thorough character of 

 his labors. 80 powerful and so free from objection was every 

 argument that no one attempted to combat them, and the con- 



