250 



Anatomy and Physiology of the 



offspring. Hence when care in selection is fully and efficiently 

 carried out, deterioration from ordinary causes does not so rapidly 

 occur. To assist in overcoming- these causes, the taking of animals 

 from different families and localities,, or ' f crossing," is adopted. 

 But even here care in selection is of equal importance. 



We have spoken of hereditary predisposition to disease : this is 

 exemplified by the fact that horses bred from " roarers" are so 

 susceptible of this abnormal state of the respiratory organs, that 

 " roaring" follows from causes which would be insufficient to 

 produce it in other horses. And experience has shown that very 

 many of the young horses sent from this county (Yorkshire) to 

 London, being in this condition, early become diseased through 

 the altered circumstances under which they are placed. That 

 which is true with regard to horses applies equally to cattle, sheep, 

 and all domestic animals. As with disease so it is also with colour ; 

 this not only becomes immediately hereditary, but passes back, as 

 it were, through several generations ; hence the necessity of looking 

 to the purity of a breed. In illustration of this position I quote 

 from Mr. Wilkinson's Letter to Sir J. Sebright, wherein we 

 read that, " suppose a number of pure Devon cows to be crossed 

 with a breed of perfectly white bulls, it is probable that some of 

 the calves would be perfectly red, others white, and the greater 

 part would partake of these colours jointly. If we were now to 

 take the red heifers produced by this cross, and put them to a 

 Devon bull, it would not be a matter of any great surprise if 

 some of their progeny, though sprung from red parents, should be 

 perfectly white, and still less that several should be mixed with 

 this colour ; though it would not, by any means, be so probable as 

 in the former instance. And were we thus to proceed through 

 several generations, this white colour would be less and less 

 apparent in the breed, but would most probably occasionally show 

 itself in some individual or other. If, on the other hand, we were 

 to breed from pure Devons only, that is, from those that have 

 been carefully bred for a great length of time, we should reason- 

 ably expect their offspring to be of the same colour with the 

 parents themselves."* 



It has often been remarked, that wild animals undergo but 

 very slight changes either in form, size, or colour ; the reason of 

 this, in many tribes, is obvious. We may take the class to which 

 deer belong as an example. At the season of rut, when the herds 

 commingle, great contentions take place between the males, by 

 which the larger number of females falls to the most vigorous and 

 healthy males, and a strong progeny is the result. Besides which, 

 many of the weaker animals not unfrequently are carried off by 

 the cold and privations of winter, thus leaving parents of good 



* " Kemarks on the Improvement of Cattle, in a Letter to Sir J. S. Sebright," 

 by J. Wilkinson. Nottingham, 1820. 



