168 NUTRITIONAL PHYSIOLOGY 



partly, it is believed, through direct influence upon the 

 kidney cells. As regards the first mode of working, it may 

 be said that the kidney is readily responsive to increased 

 blood-flow, especially if it is attended with high arterial 

 pressure. Difficulties with the heart, if they entail re- 

 tarded circulation and lowered pressure, frequently lead to 

 deficient output. 



Other Factors in Excretion. The lungs and the kidneys 

 perform so large a share in the disposal of metabolic waste 

 as to leave relatively little of the work undone. The 

 feces, however, include small quantities of miscellaneous 

 excretions, and it is assumed that the precise part borne by 

 the intestine and the liver (in the separation of bile) could 

 not be taken by the kidneys. The modified bile-pigments 

 and cholesterin of the feces illustrate this specific action. 

 The share of the skin in the removal of waste is popularly 

 overestimated. The belief that "the pores must be kept 

 open" lest poisons gather in the system is so fruitful of 

 wholesome practices that one is reluctant to question it. 

 Candor requires, however, that the physiologist repudiate 

 the moral in the story of the Italian boy, who died because 

 the surface of his body had been sealed with gold paint 

 for a few hours. If the case is authentic, he must have 

 died because of the character of the application and not 

 from toxic products of his own evolving. Volunteers have 

 submitted to have the skin shellacked and have not suf- 

 fered any other ill effects than sensitiveness to heat and cold. 



Perspiration is almost purely a mineral solution and the 

 salts it carries could doubtless be cared for by the kidneys. 

 When made profuse by severe exercise, it contains in small 

 amounts some of the organic constituents of the urine, 

 but its highest possible rating as a vehicle of nitrogen ex- 

 cretion is not impressive. The same may be said of the 

 assistance rendered by the skin to the lungs. Carbon 

 dioxid passes from the skin in measurable quantities 

 when there is abundant perspiration, but the largest loss 

 which can occur in this way seems insignificant when com- 

 pared with the discharge from the lungs. 



