DISEASE AND RELATED PHENOMENA IN ANIMAL BREEDING — 523 
for instance, for the fetus to be infected with disease at any time from the 
moment of conception to that of birth, and ante-natal infections are as 
truly acquired as are post-natal infections. It is possible for the fetus 
to be infected directly and independently of the mother, as occurs at 
times in cases of venereal disease; it is also possible for the fetus to become 
infected from the mother through the placenta, a much less common 
phenomenon. In either case, however, it is confusion of thought to speak 
of such instances as examples of the inheritance of disease. The many 
ramifications of the subject cannot be dealt with fully here; suffice it to 
say that as with acquired characters so with disease transmission the 
affirmative case has not been proven. 
The Inheritance of Predisposition to Disease.—Predisposition to 
disease may be either specific or general. In specific predisposition 
the individual is lable, should prejudicial conditions occur, to contract 
a particular disease, as for example gout, whereas general predisposition 
gives room for infection with a series of similar diseases. This latter 
type of predisposition is very commonly expressed in general consti- 
tutional debility rather than in any specific fashion. It is particularly 
shown in nervous diseases In man, where a predisposition to nervous 
derangement is expressed in a variety of ways in a given line of descent, 
but even here the predisposition is often specific to a remarkable degree. 
That predispositions are inherited cannot well be questioned, but in 
tracing their transmission it is necessary to guard against factors which 
confuse cases. Thus it does not necessarily follow that an individual 
predisposed to a disease should invariably become a victim to that disease. 
Transportation in early life to a new environment or particular attention 
throughout life to matters making for health with respect to a known 
inborn tendency may entirely overcome the predisposition. Thedegree of 
predisposition also varies; in some cases it 1s so strong as to amount 
practically to transmission of disease; in other cases it is relatively 
weak, and requires either that the inciting cause be impressed frequently 
upon the individual before resistance is broken down and the individual 
yields to attack or that some other violently unfavorable condition 
should enter into the life of the individual. 
It is worth while remarking that predisposition to disease like many 
defects of structure often skips generations in inheritance. In general it 
appears that the normal state of health is the dominant condition and 
that predispositions are for the most part dependent upon the action of 
recessive factors or sets of factors. Accordingly predisposition to disease 
is more likely to crop out as a result of consanguineous matings, because 
related individuals are more likely to bear the same recessive factors in 
their germinal material. In this fashion it is not difficult to account for 
the persistent atavistic appearance of disease in some lines of descent. 
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