

48 PHYSIOLOGICAL EEMAKKS. 



brain, on receiving information of this excess of carbon, issues 

 its mandate back again by means of the wires at its command 

 (the nerves of motion supplying the respiratory muscles), and the 

 breathing is accelerated in an exact ratio with the quantity of 

 carbon given out into the blood by the wear and tear of the 

 muscular system. 



For this reason a greyhound must be possessed, not only of 

 powerful muscles, but also of a powerful heart, to furnish them 

 with blood, in order to keep up the supply of fresh materials 

 required by their wear and tear; but he likewise requires a 

 capacious chest, for this is a measure of the quantity of air 

 which can be continually renewed by each act of breathing, and, 

 in proportion to the quantity, will be the rapidity of the com- 

 bination between the carbon in the blood and the oxygen 

 contained in the air as one of its elements. Hence, the more 

 capacious the chest, the less will be the distress occasioned to the 

 animal under violent exertion; that is, provided the heart is 

 capable of doing its duty, by circulating the blood as fast as the 

 air is supplied. No dog can be of good wind without lungs of 

 sufficient size ; but a powerful heart is also required to fulfil the 

 grand purpose of decarbonising the blood ; and from the want of 

 this arises the distress which we so often see in a badly-trained or 

 badly-reared dog. For, if the heart is never called into active 

 play by violent exercise during the period of growth, it is only 

 formed of sufficient size and power to carry on the circulation in 

 a state of repose, and then, when required for extraordinary 

 exertions, ' it is not big enough for the place,' and is incapable of 



