762 VETEEINAEY HYGIENE 



system, but this is only an index to the entire change which 

 an animal's body has undergone in being made fit for work; 

 the respiratory, circulatory, nervous and other systems are 

 affected by the change. The heart's action as the result of 

 work is rendered more active, a larger amount of blood 

 passes into the vessels, and a larger amount through the 

 lungs. 



One of the first things to occur in ' condition ' is the 

 establishment of a concordant action between the heart and 

 bloodvessels ; there must be no difficulty in the passage 

 of the blood from right to left heart, and none must exist 

 between the heart and the vessels into which its contents 

 are pumped. 



While this reciprocal action is occurring other profound 

 changes are taking place ; the body fat is being largely 

 used up and not replaced ; the muscular system is growing 

 in bulk, the muscles themselves become firmer, closer in 

 texture, and the withdrawal of their fat maps out many of 

 their contours. The tendons and ligaments throughout the 

 body, but especially below the knees and hocks, become 

 tense and firm, their outline clearly marked. The skin 

 from sweating easily in the ' soft ' horse gradually loses this 

 disposition, so that quite a considerable amount of work 

 can be done without any or only slight action of the skin ; 

 in this matter both pace and the temperature of the sur- 

 rounding atmosphere are important factors in the produc- 

 tion of sweat. 



The respirations of the ' soft ' horse which has been 

 worked are often irregular, jerky, and take a long time to 

 settle down. As the animal improves in condition all 

 irregularity of movement and jerky expirations cease, and 

 the breathing after work soon falls to normal. Eespiration 

 is a very important measure of the animal's condition. 

 Distressed respirations are due not only to the fact that 

 the lungs cannot get rid of the blood as fast as they receive 

 it, but also to the fact that its carbonic acid is not fully 

 removed, so that the muscles are not properly supplied with 



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