580 GENERAL METABOLISM. [OH. xxxix. 



such cases is to stimulate the skin to action by hot-air baths and 

 pilocarpine, and the alimentary canal by means of purgatives. 

 In some of these cases the skin secretes urea so abundantly that 

 when the sweat dries on the body, the patient is covered with a 

 coating of urea crystals. 



Varnishing the Skin. By covering the skin of such an animal 

 as a rabbit with an impermeable varnish, the temperature is 

 reduced, a peculiar train of symptoms set up, and ultimately the 

 animal dies. If, however, cooling be prevented by keeping such 

 an animal in warm cotton-wool, it lives longer. Varnishing the 

 human skin does not seem to be dangerous. Many explanations 

 have been offered to explain the peculiar condition observed in 

 animals ; retention of the sweat would hardly do it ; the blood is 

 not found post mortem to contain any abnormal substance, nor is 

 it poisonous when transfused into another animal. Cutaneous 

 respiration is so slight in mammals that stoppage of this function 

 cannot be supposed to cause death. The animal, in fact, dies of 

 cold ; the normal function of the skin in regulating temperature 

 is interfered with, and it is animals with delicate skins which are 

 most readily affected. 



CHAPTER XXXIX. 



GENERAL METABOLISM. 



THE word metabolism has been often employed in the preceding 

 chapters, and, as there explained, it is used to express the sum 

 total of the chemical exchanges that occur in living tissues. The 

 chemical changes have been considered separately under the 

 headings Alimentation, Excretion, Respiration, &c. We have now 

 to put our knowledge together, and consider these subjects in 

 their relation to one another. 



The living body is always giving off by the lungs, kidneys, and 

 skin the products of its combustion, and is thus always tending 

 to lose weight. This loss is compensated for by the intake of 

 food and of oxygen. For the material it loses, it receives in 

 exchange fresh substances. If, as in a normal adult, the income 

 is exactly equal to the expenditure, the body-weight remains 

 constant. If, as in a growing child, the income exceeds the 



