480 THE TUBERCLE BACILLUS GROUP 
tubercle formation in the mesenteric glands with lesions in other parts 
of the body. Metastatic nodules are found occasionally in the brain, 
meninges, and epiphyses of bones. 
Pathogenesis for Lower Animals. — Generally speaking, the human 
type of the tubercle bacillus is less virulent for lower animals than the 
bovine type. Monkeys in captivity, however, are susceptible to 
both types, and even infection with the avian type has been found 
in them. The course of the disease, which is spontaneous, runs similar 
to that of human consumption, with, however, a greater tendency 
toward generalized invasion. Goats, sheep, and horses are not as a 
rule infected with the human tubercle bacillus. Gattle are very 
rarely infected with the human type. Dogs and cats are said to be 
infected occasionally. 
/^afefez'fe.— Rabbits are not as susceptible to the human tubercle 
bacillus as the guinea-pig. Subcutaneous injections of the human 
tubercle bacillus usually cause only local lesions, which in the vast 
majority of instances are not fatal and clear up after some weeks. 
Massive doses, however, usually produce lesions. Intravenous injec- 
tions, unless massive doses are given, also fail to kill rabbits as a rule. 
Occasionally, however, a generalized tuberculosis with fatal termina- 
tion results. Intraperitoneal inoculations only occasionally bring 
about a generalized fatal tuberculosis. Usually slight lesions are pro- 
duced which clear up spontaneously. Ingestion of human organisms 
rarely leads to infection.^ 
6'mHea-p?"(75. — Guinea-pigs are very susceptible to infection with 
either the human or bovine tubercle bacilli, although the disease 
rarely appears spontaneously. Theobald Smith^ has shown that it 
requires but one-fifteen-hundredth as much tuberculous material to 
infect a guinea-pig as is required to infect artificial media. This 
susceptibility of the guinea-pig to inoculation with the tubercle bacil- 
lus explains the well-attested fact that inoculation of suspected tuber- 
culous material into these animals is a far more delicate test for their 
presence than attempts to grow the organisms from the same material 
on artificial media. It must be remembered in this connection that 
even dead tubercle bacilli stimulate tubercle formation in guinea-pigs,^ 
hence for an absolutely safe diagnosis, whatever tubercles are pro- 
duced in the first guinea-pig must be ground up and injected into a 
second guinea-pig. If viable tubercle bacilli are present a successful 
infection will take place, otherwise the experiment is negative. 
Suhcufaneous Inoculation.^ After ten to fourteen days a small hard 
nodule appears at the site of inoculation, and very soon afterward the 
regional lymph glands begin to enlarge and the animal begins to lose 
weight. The animal usually dies in from two to four months. Post- 
mortem, the spleen is enlarged, yellowish-brown in color, and studded 
Theobald Smith: Jour. Med. Res., 1905, 13, 253. = ibid., 1913, 27, 91. 
Prudden and Hodenpyl: New York Med. Jour., 1901, 53, 697. 
