164 NUTRITIONAL PHYSIOLOGY 



corpuscles are charged with oxygen and is independent 

 of the carbon dioxid present. 



While there is no question of the propriety of calling 

 carbon dioxid a waste-product, it does not follow that the 

 system would be benefited by its complete removal. 

 How far this is from being the case has been shown by the 

 important experiments of Yandell Henderson. He has 

 demonstrated that any considerable lowering of the carbon 

 dioxid below the high standard noted above as character- 

 istic of arterial blood results in marked prostration, often 

 involving the suspension of breathing and perhaps result- 

 ing fatally. The inference is that a certain concentration 

 of carbon dioxid is a desirable source of stimulation to the 

 nervous system and especially to the respiratory center. 

 The intimate connection between this gas and breathing is 

 manifest when its percentage in the blood is ever so little 

 increased. A noteworthy deepening of the respiration 

 promptly results. Since this is true it is not strange that 

 a reduction of the carbon dioxid should cause inhibition of 

 the breathing movements. 



Water Elimination. Water leaves "the body by all the 

 possible excretory routes. Statements regarding the 

 proportion taking this or that course can have but little 

 value, so great is the variation under different circum- 

 stances. If we exclude the effects of exercise and of un- 

 usual temperatures we may expect to find somewhat more 

 than half the whole amount to be removed by the kidneys. 

 The daily volume of the urine is customarily set down at 

 1200 to 1500 c.c. The remaining excretion of water will 

 be almost wholly accounted for by the perspiration and by 

 evaporation from the breathing passages. Of these two, 

 the former is commonly more considerable. Some loss of 

 water will occur in the feces, but normally this is not to be 

 compared with the Quantities discharged in the three ways 

 just mentioned. 



When the extern'al temperature is high the water passes 

 in increased amounts through the skin and the perspira- 

 tion may greatly exceed the urine. The urinary secretion 



