406 BIOLOGY FOR BEGINNERS 



that of their surroundings. The rate of oxidation and hence the 

 production of heat varies even more than the outside temperature 

 and this means that a heat-regulating device is required. 



Heat is required to evaporate water; therefore if moisture is 

 excreted on the surface of the skin, the body's heat is taken up in 

 evaporating it and consequently the skin is cooled. The blood 

 supply to the skin is great, the surface exposed for evaporation is 

 also large, and so by the use of the body heat to vaporize (dry off) 

 the perspiration, the blood, and hence the whole body, is cooled. 



The greater our activity or the warmer the surrounding air, 

 the larger is the amount of perspiration, and hence the greater 

 cooling effect. 



A complex system of nerve control .governs the blood supply 

 and gland activity of the skin, so that, mainly by its means our 

 temperature is kept at 98.5 degrees. The importance of this func- 

 tion of the skin is seen when we realize that a temperature of 8 or 

 10 degrees either above or below the normal is usually fatal. 



COLLATERAL READING 



Physiology Textbook, Colton, p. 381; General Physiology, Eddy, pp. 

 352-373; Applied Physiology, Overtoil, pp. 248-255; Human Mechansim, 

 Hough and Sedgwick, pp. 177-186; Human Body and Health, Davison, 

 pp. 175-190; Studies in Physiology, Peabody, pp. 232-252; Human Body, 

 Martin, pp. 215-229; Elementary Physiology, Huxley, pp. 193-247; High 

 School Physiology, Hughes, pp. 197-213. 



SUMMARY 



Waste, source, oxidation in tissues. 



Kind, carbon dioxide, water, nitrogenous compounds, salts. 

 Organs of excretion. 



1. Kidneys, location, small of back, near spine. 



Size, two by four inches, bean shaped. 



Blood supply large, high pressure. 



Ducts connecting with bladder. 



Remove water, urea, salts, etc. (3 Ib. daily). 



2. Lungs. 



Remove carbon dioxide, water, little nitrogenous waste. 



3. Liver and intestines. 



Remove bile and unused food stuff. 



