250 TUBERCULOSIS. 



the spleen being specially affected. This organ is swollen, and 

 is studded throughout by numerous tubercle nodules, which 

 may be minute and grey, or larger and of a yellowish tint. If 

 death has been long delayed, calcification may have occurred 

 in some of the nodules. Tubercle nodules, though rather 

 less numerous, are also present in the liver and in the lungs, 

 the nodules in the latter organs being usually of smaller size 

 though occasionally in large numbers. The extent of the gen- 

 eral infection varies ; sometimes the chronic glandular changes 

 constitute the outstanding feature. 



Intraperitoneal injection of pure cultures produces a local 

 lesion in the form of an extensive tubercular infiltration and 

 thickening of the omentum, sometimes attended with acute 

 tubercles all over the peritoneum. There is a caseous enlarge- 

 ment of the retroperitoneal and other lymphatic glands, and 

 later there may be a general tuberculosis. Intravenous injec- 

 tion produces a typical acute tuberculosis, the nodules being 

 usually more numerous and of smaller size, while death follows 

 more rapidly, the larger the numbers of bacilli injected. Guinea- 

 pigs, when fed with tubercle bacilli, or with sputum or portions 

 of tissue containing them, readily contract an intestinal form 

 of tuberculosis, lesions being present in the lymphoid tissue of 

 the intestines, in the mesenteric glands, and later in the internal 

 organs. 



Rabbits are less susceptible than guinea-pigs, and in them 

 the effects of subcutaneous inoculation are very variable ; some- 

 times the lesions remain local, sometimes a general tuberculosis 

 is set up. Otherwise the reactions are much of the same 

 nature. Dogs are much more highly resistant, but tubercu- 

 losis can be produced in them by intraperitoneal injection of 

 pure cultures (Koch), or by intravenous injection (Maffucci). 

 In the latter case there results an extensive eruption of minute 

 miliary tubercles. Tuberculosis can also be easily produced 

 in susceptible animals by making them inhale the bacilli. 



Varieties of Tuberculosis, i. Human and Bovine Tubercu- 

 losis. Although variations in the virulence of the tubercle 

 bacilli from different sources had been repeatedly observed, no 

 systematic comparison had up till recently been made, and it 

 was generally accepted that all mammalian tuberculosis was due 

 to the same organisms, and in particular that tuberculosis could 



