COMPOSITION OF THE BODY. 35 



nerves, glands, &c. is composed of substances that come 

 under the nitrogenous group ; " even the non-cellular 

 liquids passing out into the alimentary canal at various 

 points which have so great an action in preparing the 

 food in different ways are not only nitrogenous, but the 

 constancy of this implies the necessity of the nitrogen 

 in order that these actions shall be performed" (Parkes). 

 Albumen is a familiar example of this group. These 

 substances consist of carbon of which charcoal is a 

 well known form hydrogen and oxygen the two 

 constituents of water combined in various proportions 

 with nitrogen, and, in the case of albuminous substances, 

 with a small amount of sulphur. 



Both the fats and saccharine matters are composed 

 of certain combinations of carbon, hydrogen and oxygen. 

 In the latter, the two last mentioned elements are united 

 in the proportion that forms water, so that sugar and 

 starch may be regarded as a combination of carbon with 

 that fluid ; while in the former, there is a smaller 

 amount of oxygen. The fat, which is deposited as a 

 layer immediately under the skin, serves to maintain the 

 internal temperature of the body, by the fact of its be- 

 ing a bad conductor of heat. Fat also acts as a natural 

 elastic cushion to various parts of the system, as, for 

 instance, at the back of the eyeball, above the horny 

 frog, and around the joints. 



Dr. Carpenter remarks, that " the muscular, nervous, 

 and glandular tissues are not composed of albuminous 

 substances alone ; they contain, as an essential consti- 

 tuent of their structure, a certain portion of fat, with, 

 out which their composition, would be imperfect, and 



