BACTERIUM TUBERCULOSIS 157 



pigs. For its growth this organism requires the 

 addition of glycerin, blood serum, or egg to the ordi- 

 nary nutrient broths and jellies. It will grow only at 

 body temperature, and not at room temperature. 



It is killed by an exposure to GO C. or 142 F. in 

 thirty minutes, to 70 C. or 160 F. in ten minutes, 

 and at 95 C. or 200 F. in one minute in watery 

 suspension. Dry heat at 100 C. or 212 F. requires 

 about one hour. The organisms resist drying in the 

 dark for considerable periods. Direct sunlight kills 

 them if in thin layer or small clumps within four 

 hours. Diffused light requires two weeks for their 

 destruction. Sputum protected from direct sunlight 

 may contain living bacilli possibly for one year. Five 

 per cent, carbolic acid should certainly kill them in 

 sputum in twelve hours; in watery suspension in 

 thirty minutes. Bichloride of mercury is not of value 

 for sputum disinfection, but in strength of 1 to 1000 

 in watery suspension is fatal in one hour. No kind 

 of animal is absolutely resistant to tuberculosis, but 

 there are some that very seldom present the spon- 

 taneous disease, notably dogs and horses. 



There are four forms or varieties of the tubercle 

 bacillus: the human, bovine or cow, bird, and reptil- 

 ian. The first two only concern us, and the distin- 

 guishing features of these groups are of small impor- 

 tance here. The infectiousness of the bovine form for 

 humans has been mentioned. The human form is of 

 very low virulence for the cow, but may infect most 

 of the smaller animals. It has been found impossible 

 to obtain from any of the lower animals a serum which 

 will have a beneficial effect upon the disease in human 



