80 ORGANISM AND ENVIRONMENT 



we the means of determining the innumerable other 

 substances present in blood we should doubtless dis- 

 cover a similar delicacy of regulation. 



All parts of the body seem to participate in this 

 regulation. We have already seen how this is so in the 

 case of breathing, circulation, and the activities of the 

 kidneys and liver. Recent investigations reveal the 

 same thing in connection with such organs as the 

 thyroid, suprarenal and pituitary glands. The regu- 

 lation of the blood temperature in warm-blooded ani- 

 mals is one of the most striking instances. During 

 muscular exertion the heat production in the body 

 may be increased six or eight fold, but the tempera- 

 ture of the arterial blood is only increased by a quite 

 insignificant amount, as increase in the skin circula- 

 tion and in the evaporation of moisture from the body 

 compensates for the increased production of heat; 

 while if the external temperature is varied the effects 

 on the body temperature are also compensated by 

 changes in the skin circulation and evaporation, and 

 by variations in the heat-production of the body. The 

 regulation is through the central nervous system, and 

 is exactly comparable to the respiratory regulation of 

 the blood. 



The phenomena observed after bleeding or transfu- 

 sion of blood are of great interest in this connection, 

 and have recently been studied in some detail by 

 Boycott and Douglas, using the new method available 

 for determining the total haemoglobin and total blood 

 volume in the body during life. After bleeding the 

 total blood volume in the body is very rapidly recov- 



