Tuberculosis. 431 



lungs, liver or other organ, in the lymph glands, in the respiratory 

 or intestinal mucosa or submucosa, in the oseous cancelli, brain 

 or skin. It is, therefore, largely pathognomonic, yet it is not 

 peculiar to tubercle, being common in glanders, and other infec- 

 tive inflammations. Its presence should always lead to a search 

 for the primary tubercle nodule, with its nonvascular cluster of 

 lymphoid and giant cells and above all for the specific bacillus 

 resistant to staining. 



The tendency to extensive degeneration and caseation is especially 

 marked in swine, in which the resulting debris is often so liquid 

 that the tubercles bear a strong resemblance to abscesses. 



Calcification. The deposition of lime salts (mainly phosphates) 

 in the tubercle is a common feature of advanced cases in man and 

 pig, but especially in cattle. It is unknown in rabbits and Guinea 

 pigs. The tubercle assumes a hard cretaceous aspect and feeling, 

 grates under the knife and crepitates when pressed. This is 

 always an evidence of chronicity, but it has been observed in 

 swine in 3^ months. 



Fibroid Degeneration. Fibrosis. In this case a productive 

 fibroid inflammation takes place in the tissue of the tubercle, and 

 it is resolved more or less extensively into a hard, white, resistant 

 body. This is the pearly mass which has given rise to the name 

 of \h.^ pearl disease (perl-zucht) in Germany. It may be fibrous 

 throughout, but usually a number of the nodules show a caseated 

 centre while the external zone, that nearest to healthy tissue, has 

 alone taken on the conservative fibroid development. Like crete- 

 faction, fibrosis is an indication of chronicity in the lesion. It is 

 often seen in man, but still more so in cattle, in which it affects 

 particularly the abdominal cavity, but also to a lesser extent the 

 chest and other parts. It is remarkable for the paucity of 

 bacilli to be found in its substance, often requiring many sec- 

 tions and infinite patience to reveal the presence of the microbe. 

 This comparative lack of actively multiplying bacilli is doubtless 

 one factor, operating in the direction of conservative processes, 

 chronicity and even partial recovery. In experimental tubercu- 

 losis the extent and rapidity of development of tubercle, as also 

 of the degeneration are found to be closely allied to the number 

 of bacilli introduced. 



Cattle : Pulmonary Tuberculosis. One of the most frequent 



