Hereditary Diseases of Horses. 



125 



excess of fibrine, which is besides in a less elaborated state than 

 usual ; tubercular deposits are also found in various parts of the 

 body. This alteration in the healthy quantity and quality of the 

 albuminous ingredients of the blood, and in the integrity of the 

 various tissues, is transmitted from the parent to the offspring ; 

 and, in proportion to the amount of deviation from the normal 

 state, constitutes a scrofulous diathesis more or less decided. 

 The diathesis is strikingly hereditary,* often affecting many in- 

 dividuals of the same family, often traceable through many 

 generations, and sometimes ascribable to the sire, sometimes to 

 the dam. It is always, however, greatly aggravated (and may 

 be developed de novo) by circumstances prejudicial to health — 

 by insufficient food, by exposure to damp and to low tempera- 

 tures, and, in a marked degree, by " breeding in-and-in." By 

 this system of breeding, any inherent tendency to disease, how- 

 ever slight, is greatly aggravated, and always in a rapidly acce- 

 lerating ratio in each succeeding generation so long as the faulty 

 system is continued. 



The scrofulous diathesis affects various parts of the body, and 

 assumes different forms in different animals, and at different 

 ages in the same animal. It develops itself as rickets, hydro- 

 cephalus, tabes mesenterica, and pulmonary consumption, and 

 in these, and all its other forms, is alike hereditary. 



Rickets, like the other diseases indicative of a scrofulous habit, 

 depends on malnutrition. The bones are defective in earthy con- 

 stituents, and consequently give way under the weight which 

 they ought to sustain, becoming bent and deformed. Amongst 

 our patients, however, rickets is neither so common nor so serious 

 as in the human subject, and the young animals affected by this 

 complaint generally gain strength and vigour if they get a suf- 

 ficiently nutritive diet, and are otherwise carefully tended. 



* Dr. Watson, in his admirable ' Lectures on the Principles and Practice of 

 Physic,' thus speaks of the hereditary nature of this affection : — " In a former 

 lecture," says he, "I mentioned scrofula as one of those distempers the hereditary 

 tendency to which is indisputable. The scrofulous diathesis is hereditary : and 

 sometimes scrofulous disease is so too. I have seen lungs, taken from the body of 

 a foetus, stuffed with tubercles. There were some fine examples of this in Mr. 

 LangstafTs museum, in the city. We have, therefore, in respect to scrofula, the 



rare conjunction of congenital disease, and hereditary disposition 



Ko one, of the least observation, can doubt that the disposition to consumption is 

 very often transmitted from parent to child. We see whole families swept away 

 by its ravages. Like other hereditary tendencies, it may skip over one or two 

 generations, and re-appear in the next, just as family likenesses are known to do. 

 There are other families in which you can trace no such predisposition ; but such 

 families are perhaps few, A little leaven is sufficient, sometimes, effectually to 

 taint a whole pedigree. The tendency, however, exists in various degrees. It 

 may be so strong that no care, no favourable combination of circumstances, will 

 prevent its local manifestation ; and it may be so faint that it would never break 

 out into actual mischief if the exciting causes of scrofulous disease could be warded 

 off." — Lect. xii., vol. i,, p. 203. 



