42 
Hereditary Diseases of Sheep and Pigs. 
destruction of the parts among which they are placed. They are 
mere local symptoms of a general disorder, and are always here- 
ditary. Among pigs, however, we have never seen any truly 
cancerous tumours, though we have sometimes met with scrofulous 
tumours beaiing some resemblance to them. From the fact that 
cancerous tumours are hereditary in all animals in which they 
occur, we have no doubt that when they do occur in pigs they 
will in them likewise be hereditary. 
In conclusion, we may repeat that many of the most common, 
and some of the most serious diseases of sheep and pigs are here- 
ditary ; and that they spring from certain vices of structure or 
disproportion of parts either of a local or general nature. They 
are propagated alike, whether occurring in the male or in the 
female parent, but always most certainly, and in the most aggra- 
vated form, when occurring in both. Defects and diseases that 
have already been transmitted through several generations are 
impressed on the progeny in a most decided, permanent, and 
irremediable form. But those acquired during the lifetime of an 
individual also sometimes become hereditary, especially when of 
a constitutional nature, and accompanied by any considerable 
alteration of structure or function, or by a debilitated and dete- 
riorated state of health. Indeed debility, however produced, is 
almost certain to be hereditary ; and hence all breeding animals 
should be in a strong and vigorous condition, especially at the 
period of sexual congress. 
In fine, the successful breeder either of sheep or pigs must 
ever recollect and act upon the familiar axiom, " like produces 
like." He must therefore select his stock with the best possible 
symmetry, and with those appearances which indicate vigour of 
constitution and freedom from disease, and must continually en- 
deavour to maintain and improve excellences, and mitigate and 
remove deficiencies by judicious crossing and careful attention to 
sanatory arrangements. 
Addendum. 
Much difference of opinion prevails as to the relative influence 
of the male and female parent in determining the characters of the 
progeny. According to a very prevalent notion, the male bestows 
all valuable qualities, whether of form or of vigour ; while the 
female is regarded merely as a passive instrument which hatches, 
as it were, the male seed — an absurd doctrine long preserved 
from well merited obloquy as a convenient excuse for careless- 
ness and neglect in the selection of the female parent. A most 
ingenious hypothesis has lately been propounded by Mr. Orton of 
