34 ADVANCED PHYSIOLOGY 



which these undergo in the body much of the hydrogen 

 may combine with the oxygen to form water, H2O, while 

 the carbon also unites with oxygen to form carbon dioxid, 

 CO2. It is this combining with oxygen, this oxidation of 

 materials, which results in heat, just as it is when the 

 carbon in burning wood unites with oxygen of the air, and 

 gives off heat in making the combination. 



As will be noticed from the above formulae, fat contains 

 fifty-one parts of carbon, while sugar contains only six. Heat 

 is produced when the carbon combines with oxygen, as we 

 have said. In sugar the carbon already has six parts of 

 oxygen combined with it and cannot combine with very much 

 more. In fat, however, there are fifty-one parts of carbon, 

 and only nine parts of oxygen combined with it. In fat there 

 is therefore a much larger amount of carbon which can be com- 

 bined with the oxygen of the air than there is in sugar; when 

 fat is burned there is a large amount of oxidation and hence 

 a far greater amount of heat given off. Indeed, fat furnishes 

 a larger amount of heat than any other food. 



Thus carbohydrates and fats furnish us with a quick and 

 profitable source of energy. It must be clearly understood, 

 however, that neither of them is of any value in tissue 

 building. Neither muscle nor brain nor gland nor any 

 other active tissue can be made or even repaired by them. 



Gelatin. Most meat foods contain another material known 

 as gelatin, which in its refined form causes the hardening of 

 most of our table jellies. It is obtained from connective 

 tissues (see page 13) by boiling. In its chemical nature it 

 resembles proteid, but it will not take the place of proteid 

 in tissue building. It may be used by the body as a source 

 of energy and hence has much the same function as carbo- 

 hydrates. In eating jellies one is likely to be deceived into 

 thinking that he is eating more than he is, since they contain 

 much water and are bulky, considering the small amount of 

 actual food in them. 



