38 
Hereditary Diseases of Sheep and Pitjs. 
naturally <a very cleanly race, and indulge in wallowing in the 
mire not from any love of filth, as is generally supposed, but, 
like the elephant, rhinoceros, and other Pachydennata, for the 
purpose of protecting their skins from the attacks of insects. In 
a state of domestication, however, their condition is usually very 
different. They are cooped up in narrow, damp, and dirty styes, 
and constrained to inhale all kinds of noxious vapours, and to eat 
coarse, innutritious, and unsuitable food. We cannot then be sur- 
prised that under such circumstances they should not only become 
the victims of disease, from which in tlieir natural state they are 
free, but should also transmit to their progeny a weakened and 
morbidly-predisposed constitution. But we believe that much of 
the hereditary disease of pigs is due to another cause than that 
just indicated, viz., breeding in and in. Tliis practice is often 
pushed to an excessive and injudicious extent in these animals; 
and from their coming early to maturity, and producing a nume- 
rous progeny at one birth, it causes in them a marked deteriora- 
tion in a comparatively short space of time. In several cases 
which have come under our own observation, it has induced total 
ruin of the entire stock. At first it merely rendered the animals 
somewhat smaller and finer than before, and improved rather 
than injured their fattening properties. Very soon, however, it 
caused a marked diminution in size and vigour, and engendered 
a disposition to various forms of scrofulous disease, as rickets, 
tabes meseiiterica, and pulmonary consumption. Many of the 
boars became sterile, and the sows barren or liable to abortion. 
In every succeeding litter the pigs became fewer and fewer in 
number, and more and more delicate and difficult to rear. Many 
were born dead, others without tails, ears, or eyes ; and all kinds 
of monstrosities were frequent. Such is the complicated train of 
evils resulting from the infringement of that natural law which 
forbids sexual intercourse between animals nearly related to each 
other.* The occurrence of such effects should induce breeders 
of swine, and indeed of all animals, to practise breeding in and in 
with much caution, to adopt it only occasionally and with strong 
and healthy animals, and to recollect that, though it may improve 
Dr. Whitehead, iu speaking of the evils resulting from marriages between 
those too nearly related to each other, remarks — " A very little reiiection will 
suffice to show, that a particular temperament or disposition, prominently developed, 
and especially if existing simultaneously in both husband and wife, will be likely 
to be reproduced, still further exaggerated, in the offspring, and thus that healthy 
balance, so necessary to the harmonious discharge of the nervous and circulatory 
functions, is at length destroyed, merging itself in incapability and disease. It is 
not improbable that a succession of evils arising in this manner necessitated the 
enactment of that porti(m of the Levitical code -which prohibits intermarriage 
within certain degrees of kindred — a law which has been respected, with tolerable 
exactness, in most civilized countries, to the present day." — Whitehead on ' Some 
Forms of Hereditary Disease,' IS.")!, pp. 4, 5. 
