12 



of 136.4° ¥. ouc hour daily, for a i)eriod of six days. This method 

 insured the destruction of all living germs in the serum, without co- 

 agulating the albumen. Finally the blood-serum was subjected to a 

 temperature of 149° F. for several hours which gave a solid, trans- 

 parent jelly upon which Koch made his cultures. This was protected 

 from every |)Ossible source of contamination, and kept at the proper 

 degree of temperature and moisture. It was then inoculated by dip- 

 ping the point of a needle into the diseased tissue of the lung and 

 drawing it across the surface of the blood-serum, making :i long shal- 

 low streak. The bacilli which adhered to the point of the needle 

 were in this way dropped at intervals along tlie streak, but in such a 

 way that the subsequent growtli of each one could be seen under the 

 microscope. 



When these grew and multiplied, the point of the needle was 

 touched to them, and the adhering bacilli were transferred to another 

 layer of blood-serum for a new generation. Each bacillus grew and 

 multiplied at the point wliere it left the needle, producing around it a 

 little spherical nest of its own kind. 



By this method, Koch and his assistants were able to obtain gener- 

 ation after generation without the intervention of disease. At the 

 end of the process, which sometimes embraced successive cultivations 

 continued for six months or more, the purified bacilli were introduced 

 into the circulation of healthy animals of different species, and in 

 every instance was followed by the reproduction of the disease, while 

 other animals kept under precisely the same conditions except that 

 they did not receive the tubercle bacilli, remained perfectly healthy. 



Koch has shown, in his experiments; that this parasite requires tor 

 its development a temperature between 86° and 104° F,, and a 

 period of two weeks, so that it is only within the animal organism 

 that suitable conditions occur ; yet, as has been shown by numerous 

 observers, these plants or their spores retain their vitality outside of 

 a body, for a long time. 



Galtier made a series of experiments on the resisting power of this 

 parasite, and demonstrated that it retained its activity after being 

 subjected to temperatures ranging from 18° below freezing up to 108° 

 F. ; that it also resisted the action of water, and the dessicating pro- 

 cess, as well as strong pickle, so that the use of corned or salted beef 

 from animals affected by tuberculosis is dangerous. 



Lydtin states very positively that the virus may be taken into the 

 lungs through the inspired air, or into the digestive system with the 

 food or water, or in copulation. If this statement be true, and there 



