ETIOLOGY iSl 



tuberculous lesions. Although at the time of their discovery, 

 the tubercle bacteria from man and from animals were believed 

 to be identical, they have been found to possess slightly differ- 

 ent characters and properties. Smith pointed out in 1898, 

 that morphologically those from cattle were shorter and thicker 

 than those from man, that the growth was slightly different 

 on blood serum, and that they were much more virulent for 

 cattle and rabbits than those from the human species. Since 

 that time his conclusions have been confirmed by a number of 

 investigators. Koch obtained like results. At present, there- 

 fore, we must look upon the tubercle bacteria coming from 

 these different species as possessing races or varieties which, 

 perhaps, are the result of their different conditions of life. 

 The investigations which have been made with the decidedly 

 different forms of this organism found in tuberculosis of fowls 

 and of fish have led a few experimenters to believe that they 

 are simply varieties of the organism first described by Koch. 

 Further inquiries are necessary to fully satisfy bacteriologists 

 that all of these forms are thus related to the one species. 



to 0.3 per cent chloroform added. Discontinued sterilization was ren- 

 dered unnecessary. The temperature required to produce a sufficiently 

 firm and yet not too hard and dry serum is for the dog 75° to 76° C. For 

 horse serum it is from 4° to 5° lower. The serum was set in a thermo- 

 stat into which a large dish of water was always placed to forestall any 

 abstraction of moisture from the serum. About 3 hours suffice for the 

 coagulation. ^Vhen serum containing chloroform is to be coagulated, I 

 am in the habit of placing the tubes for an hour or longer in a water 

 bath at 55° to 60° C, or under the receiver of an air pump, to drive off 

 the antiseptic. This procedure dispenses with all sterilization excepting 

 that going on during the coagulation of the serum. It prevents the 

 gradual formation of membranes of salts, which, remaining on the sur- 

 face during coagulation, form a film uusuited for bacteria. Tubes of 

 coagulated serum should be kept in a cold closed space where the 

 opportunities for evaporation are slight. They should always be kept 



inclined. « 



"The ordinary cotton-plugged test tubes I do not use, because of 

 the rapid drying out permitted by them, as well as the opportunities for 

 infection with fungi. Instead, a tube is used which has a ground glass 

 cap fitted over it. This cap contracts into a narrow tube plugged with 

 glass wool. This plug is not disturbed. The tube is cleaned, filled, and 



