402 



POINTS. 



of the muscles. The limbs, strained by the constant necessity of the 

 position, soon become crippled, while excessive labor causes the flesh to 

 waste ; hence the miserable objects which are sometimes witnessed toil- 

 ing along the thoroughfares of the metropolis. 



DIAGRAMS, ILLUSTRATING THE DIFFERENT CAPACITIBa OP THE OPPOSITE FORMATIONS OF THORAX. 



firi a» 



THE THORAX OP A CART HORSE. 



THE THORAX OF A BLOOD HORSE. 



A A. The capacities of the two chests in the quiet condition. 



B B, B B. The limits of expansibility in each, when excited. 



cc, c c. The outside of the coat in the quiet condition. 



dd,dd. The surface of the body in the excited state. 



To render the above facts comprehensible to the generality of readers, 

 let it be granted that the lungs of the cart and of the blood horse, when 

 expanded to the uttermost, would occupy the like space. When not ex- 

 cited, or both being of the normal size, the respiratory apparatus of the 

 coarser breed is by far the larger of the two. In the passive condition, 

 the heavy quadruped inhales much more oxygen than is needed to vivify 

 the blood. The excess is, therefore, appropriated by the food and nour- 

 ishes the frame ; hence dray horses have a tendency to become fat. On 

 the contrary, in the ordinary mood, the lungs of the thorough-bred re- 

 ceive scarcely more air than is required to uphold vitality; therefore 

 this kind of quadruped exhibits, as a general rule, no vast disposition 

 toward excessive obesity. 



During all quickened movements, however, the action of the lungs 

 and the speed of the circulation are much increased. The impetus 

 given by motion to the vital fluid causes the detention in the lungs to 



