640 
HEREDITARY DISEASES OF HORSES. 
affecting many individuals 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 temperatures, and, in a marked degree, by 
“ breeding in-and-in/’ By this system of breeding, any 
inherent tendency to disease, however slight, is greatly 
aggravated, and always in a rapidly accelerating 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, hydrocephalus, 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 constituents, 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 sufficiently nutritive diet, 
and are otherwise carefully tended. 
Hydrocephalus , or water in the head, in one of its forms, is 
a tuberculous inflammation of the internal serous membranes 
of the brain. It is ushered in by languor, disordered di- 
gestion, irregularity of the bowels, and a falling off in con- 
dition. The limbs become weak and tottering; the head is 
hot and tender, and held in a dependent position ; the eyes 
are impatient of light, and the pupils partially closed ; there 
is more or less fever and an accelerated pulse. These symp- 
toms, indicative of active inflammation, give way, after a 
in Mr. Langstaff’s museum, in the city. We have, therefore, in respect to 
scrofula, the rare conjunction of congenital disease, and hereditary disposition. 
. . . . No 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 reappear in the next, just as family like- 
ness 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 favorable combi- 
nation 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. 
