MINUTE STRUCTURE. 257 



membranes generally, and in the tissues of the alimentary canal ; 

 in the pleura, peritoneum, and arachnoid; in the structure of the 

 lymphatic glands, particularly the mesenteric and the cervical ; 

 also in the lungs, spleen, liver, etc. It is characteristic of this 

 disease that it attacks many organs, and that in cases of acute 

 tuberculosis miliary tubercle is encountered in nearly every 

 organ of the body, 



b. Minute Structure. — Although the minute anatomy of 

 tubercle has been most patiently wrought at for ^^ears, perfect 

 agreement on this point, as also the parts which the several 

 histological elements play, has not, in our day, been arrived 

 at. The chief elements of tubercle may be stated as : 

 1. Lymphoid elements — small round bodies, slightly granular, 

 and containing a single nucleus ; 2. Epithelial cells, rather 

 large and delicate ; 3. A giant cell, consisting of a granular 

 mass of protoplasm with many nuclei, and processes stretching 

 in different directions — this, together with other fibres, forming 

 a hyaline structure or meshes ; 4. Intercellular matter of 

 varying character ; 5. Free nuclei. Opinion differs as to the 

 relative proportion and relation of these several elements. 

 Probably age of the product, as also situation, may have some 

 influence in both these directions. 



Although possessed of neither vessels nor lymphatics of its 

 own, tubercle is liable to undergo retrogressive changes : 

 (a) It may be softened and absorbed; (6) it may calcify; 

 (c) it may undergo fibroid change. 



Occurrence in the Horse. — That this constitutional condition 

 of scrofula may in our patients exhibit itself in the form of 

 acute tuberculosis is not impossible. The probabilities, how- 

 ever, in adult life are largely in favour of its appearance as 

 localized tubercle, although even in this development I am 

 rather doubtful if I have ever encountered it. When exhi- 

 biting itself in this latter form, the situations are chiefly the 

 lungs and pleura, with the gland-structures of the abdomen. 

 In all such developments its diagnosis is rather diflicult, seeing 

 that such changes simulate and may be mistaken for those the 

 result of common inflammation, or other textural alterations 

 connected with special diseased processes. The nearest 

 approach to true miliary tubercle in the organs of the horse is 

 probably the diffuse granulation masses found m the lungs 



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