TUBERCLE BACILLUS 481 
with tubercles, some minute and gray, others larger, yellowish and 
frequently caseous. The regional lymph nodes also have usually 
undergone caseation, particularly the inguinal glands, less com- 
monly the axillary glands. The liver usually has a few rather large 
caseous or fibrinous tubercles, particularly on the free border. The 
kidneys also may have a few tubercles. If the animal has lived two 
or three months the thoracic cavity is also invaded, and scattered 
miliary tubercles may be seen on the lungs. The mesenteric, bronchial, 
sternal and cervical glands are invaded. 
Intraperitoneal Inoculation.— The disease runs a more rapid course, 
death usually taking place in from three to eight weeks. The peri- 
toneum is chiefly involved, particularly when death takes place early. 
The omentum is thickly studded with tubercles which tend to become 
confluent and to caseate. Certain mesenteric glands also enlarge and 
become caseous. As in the subcutaneous inoculation, the inguinal 
and axillary glands may be involved, but the lesions do not progress 
so far. 
Ingestion.— The lesions usually resemble those of intraperitoneal 
infection, with, as a rule, marked lung involvement. 
Inhalation and Pulmonary I nondation.— The lungs contain con- 
fluent tubercles, many of which are caseated. Not infrequently one 
or more entire lobes may be involved. Cavity formation, however, 
is uncommon. The abdominal ^'iscera, particularly the spleen, are 
involved, as well as the regional lymph glands. 
Products of Clinical Importance Derived from the Tubercle Bacillus. 
— Old Tuberculin (O. T. Koch). i — A four to six weeks' pure culture of the 
tubercle bacillus grown in o per cent glycerin broth is killed by heat- 
ing to 110° C. for one-half hour, and then evaporated to one-tenth its 
original volume on the steam bath. It is then filtered through sterile, 
unglazed porcelain filters. The resulting fluid, wdiich is dark brown 
in color, syrupy in consistency, and which keeps in the vndihded con- 
dition in the cold and away from sunlight for months apparently 
unchanged, is known as old tuberculin. Old tuberculin contains the 
water and glycerin-soluble products of metabolism of the tubercle 
bacillus and products of autolysis of tubercle bacilli which are not 
precipitated by heat, as well as unchanged concentrated constituents 
of the broth and about 50 per cent of glycerin: 0.25 to 0.5 per cent 
tricresol is added as a preservative. The nature of the reactive 
substance or substances in tuberculin is unknown. (For discussion 
see Long, "Tubercle," 1924.) The composition of tuberculin even 
when prepared by a uniform technique appears to be variable.- Tuber- 
culin prepared from the human type of the tubercle bacillus is acid in 
reaction; that from the bovine type is alkaline.^ 
1 Koch: Deutsch. med. Wchnschr., 1890, 16, 1029; 1891, 17, 101. 
2 White and Hollander: The Chemical Composition of Commercial Tuberculins, 
Trans. Ninth Ann. Meet. Natl. Assn. Study and Preven. Tuberculosis. 
^ Theobald Smith: Jour. Med. Res., 1905, 13, 405. 
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