414 A MANUAL OF VETERINARY PHYSIOLOGY 



of horses to overstep the mark and produce ■ stateness,' a result 

 which, like the fatigued muscle on the myograph, is usually 

 recovered from by a short judicious rest, to which the system 

 immediately responds. 



During training all superfluous fat and water are removed 

 from the body, the muscle -substance is built up, and the respira- 

 tory capacity increased. It is very necessary to remember that 

 condition, though judged of largely by the state of the muscles, 

 has a very important claim on the respiratory and circulatory 

 systems. To sustain severe and prolonged muscular exertion an 

 adequate supply of oxygenated blood must be sent to the muscles ; 

 this necessitates a rapid flow of blood and adequate ventilation 

 in the lungs, with strong regular pumping power in the heart ; 

 all these factors must work in harmony. As a matter of fact, the 

 ability to endure the strain of a violent muscular effort is far 

 more dependent on the training of the respiratory and cardiac 

 mechanisms than on that of the muscles. Long walking exercise 

 is given as a muscle developer, and judicious gallops to give an 

 animal its ' wind,' yet as a matter of fact the ' wind ' is largely a 

 question of heart. As the circulatory pump works at high 

 pressure, the bloodvessels must be fit to stand the strain and to 

 return to the heart at both auricles the amount of blood leaving 

 by both ventricles. A deficiency in this mechanism leads to 

 ' loss of breath ' ; clogging in the lungs means deficient oxygena- 

 tion in the tissues, and without an adequate supply of oxygen the 

 muscles are powerless to contract. We are clearly shown, from 

 what may be witnessed in the hunting-field, or wherever horses 

 are exposed to long-continued strain, that the chief value in 

 training is located in the functional improvement of the muscular 

 tissue of the heart and in the circulatory system in the lungs ; 

 both of these have to be educated to withstand the extra strain 

 imposed and to work economically. The voluntary muscles 

 have also to be educated to work in the best and most economical 

 manner ; they must be used to advantage, smoothly and in 

 combination ; their response must increase in rapidity and power, 

 while their relaxation must not be too prolonged and so cause 

 loss of time. Unpractised movements are a serious source of 

 waste ; by practice the same amount of work can be performed 

 with a reduced expenditure of energy, and this is true for both 

 men and horses. 



Sherrington* points out that in properly balanced muscular 

 movements there is a period of rest between each successive 

 contraction, which is recuperative in nature and opposed to 

 fatigue. One feature in training, which will be more fully appre- 

 ciated when the study of the nervous system has been made, is 



* ' The Role of Reflex Inhibition,' Science Progress, No. 20, April, 191 1. 



