472 THE TUBERCLE BACILLUS GROUP 
infectious for some time. In order to determine that tubercle bacilli 
are killed it is necessary to inoculate the material containing them 
into guinea-pigs, the guinea-pig being far more sensitive than artificial 
media for this purpose. Theobald Smith' has shown that it takes at 
least fifteen hundred times as many tubercle bacilli to infect artificial 
media as it does to infect a guinea-pig. It must be remembered that 
even killed tubercle bacilli, as Prudden and Hodenpyl- have shown, 
produce tubercles in guinea-pigs, but that these tubercles are not trans- 
missible to other guinea-pigs; consequently it is necessary to inoculate 
a second set of guinea-pigs from the tubercles developing in the first 
set of pigs in order to be certain that the bacilli are killed. 
Products of Growth. — Enzymes.— Tubercle bacilli do not produce 
soluble proteolytic enzymes. Xo carbohydrate-splitting enzymes 
have been observed. 
Carriere,^ and Wells and C'orper* have shown that the bodies of 
tubercle bacilli contain a lipase of moderate activity. Kendall, Walker 
and Day^ have demonstrated that the filtrates of cultures of human and 
bovine tubercle bacilli contain a soluble esterase; the action of the 
enzyme upon fats is relatively slight. This esterase is produced in 
an active form in media of very simple composition." 
Winternitz and IVIeloy^ have shown that the lipase (esterase?) 
activity of the blood is decreased in tuberculosis. Bauer states it is 
increased in the early stages of the disease. 
Hemolysis.— Kayhaud and Hawthorn^ state that cultures of tubercle 
bacilli will not hemolyze the erythrocytes of normal guinea-pigs; the 
erythrocytes of tuberculous pigs, however, are hemolyzed. 
Tubercle bacilli do not form indol or the ordinary products of bac- 
terial decomposition in ordinary media. They do not liquefy gelatin 
nor do they coagulate milk. Theobald Smith^ has called attention 
to a very' constant differential character between the human and 
bovine types of the tubercle bacillus. In glycerin broth the human 
tubercle bacillus causes a permanent acid reaction, while the bovine 
bacillus under the same conditions causes the medium to become 
alkaline if the growth conditions are suitable. Kendall, Day and 
Walker'** have studied the metabolism of a few typical bovine and 
human strains, and find that the acidity of the human cultures is due 
apparently, in part at least, to the utilization of the glycerin for energy, 
thus sparing the protein of the medium. The bovine bacillus does not 
appear to be able to utilize glycerin for energy, hence it derives its 
energy from the protein constituents of the medium, forming therefrom 
basic substances which are alkaline in reaction. Tuberculin prepared 
1 Jour. Med. Res., 1913, 28, 91. '' New York Med. Jour., 1891, 53, 697. 
3 Compt. rend. Soc. de Biol., 1901, 53, .320. 
4 Jour. Infec. Dis., 1912, 11, 388. ' Ibid., 1914, 15, 443. 
« Kendall, Walker and Day: .Jour. Infec. Dis., 1914, 15, 455. 
' Jour. Med. Res., 1910, 22, 107. 
8 Compt. rend. Soc. de Biol., 1903, 55, 403. 
9 Trans. Am. Phys., 1903, 18, 108; Am. Jour. Med. Sci., 1904, 128, 216; Jour. Med. 
Res., 1905, 13, 253, 405. 
1" Jour. Infec. Dis., 1920, 26, 45, 77. 
