IIORSE-BACK RIDING. 49 



It is easy to explain the activity of the respiration 

 while riding. The normal number of respirations in 

 a minute is set down at i8 in the adult, but I have 

 found it to be 28 to 32 after a fifteen-minute French 

 trot. The English trot produces a little smaller 

 result. Under certain particular conditions, the num- 

 ber has risen to 55 in a minute. In a very rapid gait 

 the respiration becomes short and frequent. 



Mr. Smith has thus tabulated the effect of mus- 

 cular exercise upon the quantity of air which enters 

 the lungs at each respiratory movement : 



Lying down I • 00 



Standing 1-38 



Walking (a mile an hour) 1-90 



Riding (at a walk) 2-20 



Walking (two miles an hour) 2-76 



Riding (at a gallop) 3 • 16 



Riding (at a trot) 4-05 



Swimming 4* 32 



Running (seven miles an hour) 7-00 



If it is conceded that a man takes half a litre of 

 air into his lungs at each inspiration when at rest, he 

 would take nearly double as much when walking his 

 horse — or one litre ; two when trotting ; but in a 

 gallop, when the reaction is a little less than trotting, 

 he would take one and a half. Enlargement of the 

 thoracic cavity is often observed in horsemen ; this 



