426 MYCOBACTERIUM 



The subcutaneous injection— usually made in the left thigh — of either human or bovine 

 bacilli, even in minute doses, is followed by death from generalized tuberculosis in about 

 6 to 15 weeks. At necropsy, there is a caseous local lesion ; the superficial inguinal, and 

 often the femoral, glands are much enlarged and caseous ; the sublumbar, portal, medias- 

 tinal, and bronchial glands are enlarged and generally caseous ; the spleen is greatly 

 enlarged, and is beset with irregular necrotic areas, varying considerably in size, of a 

 yellowish-white waxy appearance ; the Uver is enlarged and contains smaller necrotic 

 areas of a yellow or greenish colour ; the lungs contain small numbers of rounded gelatinous 

 tubercles. The most striking appearance is afforded by the necrotic areas in the spleen 

 and liver ; these are peculiar to the guinea-pig. They are more marked after injection with 

 bovine than with human bacilli. True tubercles are not often seen except in the very 

 early stages of the disease, and in the lungs. It wUl be noted that the distribution of 

 lesions is quite different in the guinea-pig from that in the rabbit. In the rabbit they are 

 most marked in, and often confined to, the lungs and kidneys ; in the guinea-pig the 

 lymphatic glands, spleen, and liver bear the brunt of the disease ; the lungs are but sUghtly 

 affected, and the kidneys practically never. 



Intraperitoneal injection of human or bovine baciUi is followed by death in 2 or 3 weeks. 

 Post mortem, there is a local caseous abscess in the abdominal wall ; the superficial inguinal 

 glands are enlarged and caseous ; the omentum is rolled up, thickened, and caseous ; the 

 portal and often the mediastinal glands are enlarged and caseous ; and the spleen and liver 

 may show small foci of necrosis. The effect of intravenous inoculation of minimal doses 

 has been described by Fust (1938). 



There is a disease that occurs naturally in guinea-pigs known as pseudotuberculosis ; 

 it is caused by Pasteurella pseudotuberculosis {B. pseudotuberculosis rodentium). The lesions 

 to which it gives rise include white rounded nodules in the spleen, liver, and mesenteric 

 glands. These are unlike the necrotic lesions caused by the true tubercle bacillus, but 

 may confuse those who are not well acquainted with the disease, especially since, when 

 inoculated subcutaneously into normal gumea-pigs, the pseudotubercle bacUlus gives rise 

 to a local lesion and caseation of the focal lymphatic glands. The differential diagnosis 

 can be made by microscopical and cultural examination. Microscopically, short, non- 

 aoid-fast, Gram-negative, bipolar-stained bacilli are seen, though often only in small 

 numbers ; culturally these organisms grow readily on ordinary media within 24 hours (see 

 Chapter 32). 



Mtirine bacUh are much less pathogenic for the guinea-pig than the other two mam- 

 maUan types. Relatively large doses, 01 and 1-0 mgm., intraperitoneaUy may cause 

 death from acute or chronic atypical generalized tuberculosis ; but smaller doses intra- 

 peritoneaUy, and subcutaneous doses up to 5 mgm., give rise to no more than retrogressive 

 lesions remaining more or less localized to the site of inoculation. 



Avian baciUi are very much less virulent for the guinea-pig than the human and bovine 

 types. Subcutaneous injection is followed by a local abscess and sweUing of the regional 

 glands ; death is unusual unless a large dose is given. Intraperitoneal injection of large 

 doses is followed by death in a few weeks. Post mortem, the omentum is thickened, the 

 spleen is large and red, there are minute grey points in the liver, and there may be fluid 

 in the pleural cavities. Though neither after subcutaneous nor intraperitoneal injection 

 are macroscopic tubercles visible, smears or cultures made from the spleen and fiver will 

 generaUy reveal the presence of tubercle bacilli — Yersin type of disease. 



Rats and Mice. — In the past these animals have been regarded as comparatively 

 resistant to tuberculosis. More recent work, however, particularly with mice, seems to 

 show that their resistance has been rather overestimated. Subcutaneous inoculation, 

 except in large doses, seems to have Uttle effect. Intraperitoneal inoculation of mice with 

 1 mgm. of human or bovine baciUi sets up a disease usuaUy proving fatal in 3 to 4 weeks, 

 whUe intravenous inoculation with 0-2 mgm. is often fatal in 2 to 3 weeks. Post mortem, 

 the lungs are studded with translucent, gelatinous, mUiary tubercles ; simUar tubercles 

 are sometimes present on the pericardium ; the spleen shows a variable degree of enlarge- 



