57(> RESPIRATION THE SOURCE 



ceterisparibus,that he obtains more caloric from 

 the atmosphere by respiration ; that his blood is 

 richer and more abundant ; and that his compo- 

 sition is renewed more rapidly, or in about sixty 

 days. 



Again ; that the aggregate vital energy of the 

 horse is greater, in proportion to his size, than 

 that of man, would appear from the following 

 facts : First, that his tractive power has been 

 found equal to that of six men, whose collective 

 weight is about six times 150 Ibs. making in all 

 900 Ibs. ; whereas that of the horse has been es- 

 timated at an average of only 700 Ibs. Secondly, 

 that a man in full health, weighing 150 Ibs. di- 

 gests about 1^ Ibs. of actual nourishment daily, 

 which is only about T ^ of his whole weight, and 

 much less than what we have seen to be the 

 ratio consumed by the horse. From which it 

 follows, that, in a state of the most vigorous 

 health, man requires above three months for the 

 renewal of his organization, allowing that all his 

 actual nourishment is converted into blood and 

 his several tissues.* Coinciding with the above 



* It is here worthy of notice, that, before chyle is converted 

 into blood, it must give off more or less carbon and hydrogen in 

 the lungs ; so that the quantity of blood generated must be pro- 

 portionally less than that of the food consumed. The difference, 

 however, is small, and cannot materially aftect the foregoing cal- 

 culations, which may be regarded as a sufficiently near approxi- 

 mation to the truth, as will be shown when I come to the influence 

 of food on respiration. 



