SECRETION. 69 



entire volume of blood, and the venous blood returning from it is charged 

 with waste matters, and its temperature is increased. 



2. The muscular tissue, on account of the many chemical changes occur- 

 ring during active contractions, must be regarded as the chief heat- 

 producing tissue. 



3. The secreting glands, during their functional activity, add largely to 

 the amount of heat. 



The entire quantity of heat generated within the body has been demon- 

 strated experimentally to be about 2300 calories, a calorie or heat unit 

 being that amount of heat required to raise the temperature of one kilo, of 

 water (2.2 Ibs.) one degree Centigrade. This quantity of heat if not utilized 

 and retained within the body would elevate its temperature in 24 hours 

 about 60 F. That this volume of heat depends very largely upon the 

 oxidation of the food stuffs can be shown experimentally. 



The normal temperature of the body is maintained by a constant expen- 

 diture of the heat in several directions : 



1. In warming the food, drink and air tfcat are consumed in 24 hours. 

 For this purpose about 157 heat units are required. 



2. In evaporating water from the skin and lungs; 619 heat units being 

 utilized for this purpose. 



3. In radiation and conduction. By these processes the body loses at 

 least 50 per cent, of its heat, or 1156 heat units. 



4. In the production of work ; the work of the circulatory, respiratory, 

 muscular, and nervous apparatus being performed by the transformation of 

 369 heat units into units of work. 



The nervous system influences the production of heat in a part, by 

 increasing the amount of blood going through it by its action upon the 

 vasomotor nerves. Whether there exists a special heat centre has not 

 been satisfactorily determined, though this is probable. 



SECRETION. 



The Process of Secretion consists in the separation of materials from 

 the blood which are either to be again utilized to fulfill some special pur- 

 pose in the economy, or are to be removed from the body as excrementi- 

 tious matter ; in the former case they constitute the secretions, in the latter, 

 the excretions. 



The materials which enter into the composition of the secretions are 

 derived from the nutritive principles of the blood, and require special 



