Breeding Power and Sterility. 121 



quantity and deteriorated quality of tlie general circula- 

 tion. 



Breeding power in animals varies with activity, and the 

 quantity of a good quality of blood. Bulls may be fertile 

 when used with only a few cows, but may not be fertile 

 with many rather fat cows ; or bulls may be fertile and in- 

 fertile by turns, when too fat, according to the transient 

 quality of their blood, the blood quality rapidly improving 

 or deteriorating according to exercise and blood vitaliza- 

 tion by breathing, which is shown in the practice of driv- 

 ing ; as, from Prof Tanner's account, was practiced with 

 cows by James Webb — the eminent sheep breeder — 

 and some other breeders in England, and is resorted to in 

 some instances in this country, with results that usually 

 insure breeding. The increased extent of breathing that re- 

 sults from driving and greater activity, increases the leading 

 vital quality — the oxygen — which makes a larger propor- 

 tion of the blood available for organization, even a small 

 improvement in quality of blood, in this way, being suf- 

 ficient to change the condition, by maturing previously 

 immature ova ; and as heat is developed in the tissues, 

 and circulated in the blood according to activity, the in- 

 creased heat arising from exercise in proximity with the 

 ova may in some cases soon change infertility to fecun- 

 dity. 



But it is neither necessary nor expedient to take any such 

 risk, as moderate regular exercise, every day, would change 

 the uncertain narrow margin of varying chance into a 

 broad path of established certainty of breeding. 



We see this principle well illustrated in the active mus- 

 cular breeds of animals, even in large cattle, as in many oi 

 the Herefords, that have a fair share of muscularity, and 

 retain their full circulation and breeding power by mod- 

 erate but regular exercise. 



