314 STUDIES IN ADVANCED PHYSIOLOGY. 



explosives the nitrogenous proteids of the body are a mild 

 form of explosive out of which, under proper circumstances, 

 large amounts of energy may be utilized. The discussion 

 of the manner, however, in which it is believed to be done 

 is postponed to the chapter on nutrition. 



2. The Albuminoids. The albuminoids resemble the 

 albumens or proteids in containing nitrogen. The nitrogen, 

 however, seems in such a combination as not to be avail- 

 able to the body as food, as it is in the case of the proteids. 

 For this reason the albuminoids are not able to replace the 

 proteids. The most familiar example of the albuminoids is 

 gelatine found in soups or used in numerous desserts. This 

 gelatine is derived from the connective tissues.. It contains 

 carbon, oxygen, hydrogen, nitrogen, and traces of other 

 substances, resembling, therefore, as just stated, the pro- 

 teids ; but the contained nitrogen seems not to be assimila- 

 ble by the tissues, and so this food must figure in the 

 body rather like a non-nitrogenous than a nitrogenous food. 

 Regularly, however, the amount of albuminoids taken as 

 food is so small that it does not figure materially in the 

 economy of the body at all. 



3. Carbohydrates. In the carbohydrates are included 

 the starches and sugars. The name "carbohydrates" 

 naturally suggests carbon and water as entering into their 

 composition, and such is, in a certain sense, true. All 

 carbohydrates are composed of carbon, hydrogen and oxy- 

 gen, but the hydrogen and oxygen are present in the pro- 

 portion of water; that is, two atoms of hydrogen to every 

 one atom of oxygen. An important point is that they con- 

 tain no nitrogen. The composition of the commoner car- 

 bohydrates will easily explain this. Thus the composition 

 of cane sugar is, Ci 2 H 2 2 On; of glucose, C c Hi 2 O G ; 

 of starch, C 6 H 10 O 3 . 



The physiological value of these foods lies in the fact 

 that they figure as sources of energy. It will be pointed 

 out in the following chapter that probably the main source 



