4 

 treatment with acids, a characteristic which separates it from 

 all other known forms of germs, with the exception of the germs 

 of I^eprosy. 



Dr. Koch found that these germs would only grow under 

 certain definite conditions. As soon as he found in the sputum 

 any tubercles (the tubercle is the diseased spot caused by the 

 presence of the tubercular germ,) it became necessary to ascer- 

 tain whether they were the actual cause of the disease or only 

 happened to grow after the disease had become established. 



To determine this point some of these germs were grown in 

 glass tubes containing a mixture of gelatine and broth, and 

 were kept in them at a regular temperature of about 99° F., for 

 some weeks. On this nutrient medium the germs grew, and 

 after a time the appearance they presented was that of a gray 

 membrane extending over the surface. Some of the germs 

 were then taken from these glass tubes and planted in other 

 glass tubes and grown under similar conditions. 



This was repeated a number of times, so that there was no 

 possibility of any other germs being present in the last tubes. 



A number of germs were taken from one of the last tubes, 

 and introdu.ced into the body of a healthy animal ; in some cases 

 they were injected under the skin; in other cases they were in- 

 jected into the veins or abdomen ; and in others, again, the 

 germs were mixed with the food given to the animals. 



The result was that in the course of a short period, a month 

 or two, the animals were killed and a post mortem examination 

 made, revealing the presence of the disease in various parts of 

 the body, containing the same sort of germs as inoculated. 



These experiments established the fact that these germs are 

 the cause of Tuberculosis, both in the human and bovine fam- 

 ilies. 



The following are among the chief accessory causes : 



HEREDITY. 



Tuberculosis may be inherited, but in what way and how 

 often are unsettled problems. The rarity with which it occurs 

 may be gathered from the fact that out of 15,500 calves killed 

 at the Berlin slaughter house there were only four calves that 

 had Tuberculosis. 



This would seem to prove that neither the sire or dam, if 



