1894.] Animal Mechanics. 565 
and one of the first essentials to be considered is that of 
stamina and constitution, or, in other words, the capacity for 
hard work and: powers of endurance, or the same qualities in 
this respect that all working animals should possess. 
These qualities are largely determined by heredity, and 
selections for breeding purposes should be made with reference 
to these qualities in the ancestors. Good sanitary conditions 
must of course be maintained, to secure a continuance of 
robust health and an active performance of the normal func- 
tions of nutrition. 
PREPOTENCY. 
Strength of constitution or powers of endurance must not 
be confounded with prepotency, or the quality of holding a 
preponderating influence in the act of reproduction. Many 
animals that are prepotentin transmitting their own qualities, 
are deficient in constitution, and their offspring lack that 
active and vigorous performance of the nutritive organs that 
is essential to stamina and powers of endurance in useful 
work. Prepotency arises from uniformity in the characteris- 
tics of ancestors for many generations, and these characters 
may or may not be desirable. 
In the improvement of the pure breeds with their present 
high development of valuable qualities, an accumulation of 
slight variations must be the aim. We cannot expect to gain 
any wide departure from present characters at a single step. 
Progress can only be made by a succession of short steps, and 
their sum will represent the real advantage gained. Small 
items determine the difference between gain and loss in the 
present activity of the industries, and in agriculture we must 
recognize the importance of slight improvements in each 
detail of general management as the only available method 
of making real progress. 
BREEDING TO A TYPE. 
In making selections for breeding, an ideal type of excel- 
lence representing definite valuable qualities, should be strictly 
