132 TUBERCULOSIS 



ordinary tuberculous lesions. Although in the beginning, the 

 tubercle bacteria from man and from animals were believed to 

 be entireh' identical, they have been found to possess slightly 

 different characters and properties. Smith pointed out in 

 1898, that morphologicalh' those from cattle were shorter and 

 thicker than those from man, that they grew 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 has recently obtained like results. At 

 present, therefore, we must look upon the tubercle bacteria 

 coming from these different species as possessing races or 

 varieties which, perhaps, are the results of their different con- 

 ditions of life. The investigations which have been made 

 with the decidedly different forms of this organism found in 

 in tuberculosis of fowls and offish have led a few experimen- 

 ters 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 re- 

 lated to the one species. There seems to be no reason for 

 doubting that the bovine and human forms are varieties or 

 races of the same species. The difference in the conditions of 

 life under which the}' exist in the bodies of men and of cattle 

 are quite enough to explain resulting differences in the 

 bacteria. 



coagulation. When 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 ex- 

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

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

 surface during coagulation, form a film unsuited for bacteria. Tubes of 

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

 tunities 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 



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