222 THE DISEASES AND DISOEDERS OF THE OX. 



no doubt that a great deal of the bovine tuberculosis which 

 exists is due to this avoidable cause, and it is equally indubitable 

 that a similar course of action also leads to a most objectionable 

 result in the case of horses, namely, the prevalence of ** roarers." 



We have, in the first place, to complete our account of the 

 changes which have taken place in the case of oxen which have 

 died of the malady we are discussing. After death the tuber- 

 cular deposits can be examined, and thus we are enabled the 

 better to understand the nature of the disease. It has been 

 found that the centre of each tubercle of a human being is taken 

 up by small, round, wrinkled, granular, cells, which are not 

 present in bovine tubercles. This point of difference, however, 

 does not make us quite certain to what extent we ought to 

 consider human tuberculosis as different from the closely similar 

 disease of oxen. 



Inside the tubercles there are no blood-vessels ; but around 

 them and in the interstices of the masses of tubercles these 

 channels by which they, like all other structures, normal or 

 abnormal, are supplied with new material are fairly numerous. 

 The tubercles themselves, therefore, never become large, but 

 they are continually surrounded by newly-formed ones, and the 

 tubercular masses thus produced may at length weigh several 

 pounds. The student of comparative pathology will recollect 

 that, in this matter of blood-supply, tubercular masses are to be 

 distinguished from the class of malignant tumours known as 

 ''sarcomata." 



Tubercles may become impregnated with earthy matter, and 

 when thus calcified they are like little yellowish, stones about as 

 large as peas ; and if crushed, they resemble pieces of chalk. If 

 cut through, a larger petrified portion in the centre is seen to be 

 surrounded by a fibrous layer on the outside. The earthy 

 matter consists mainly of the insoluble phosphates and carbo- 

 nate of lime, together with a small quantity of soluble salts 

 of sodium. 



A tubercle, before it is calcified, contains mainly albumen, 

 with a little fibrin and fat. Now, whether the tubercles do or 

 do not calcify, they frequently soften and become caseous. 

 This softening begins in the centre, and travels towards the 

 circumference of the tubercle. If calcification preceded the 

 softening, the matter in the centre is found to be white, and to 



