NON-XITROGEXIZED PRINCIPLES. 379 



nivora, for example, may be well nourished upon a diet com- 

 posed exclusively of nitrogenized matter ; and the remarks 

 we have just made upon training show that the human 

 subject may be brought to a high condition of physical 

 development, when starch, sugar, and fat are almost en- 

 tirely eliminated from the food. This shows conclusively 

 that the division of the food into plastic and calorific ele- 

 ments is not absolute, and that the animal temperature 

 may be maintained without the hydro-carbons. The nitro- 

 genized principles certainly are the only class of alimentary 

 substances capable of forming muscular tissue ; but, by cer- 

 tain transformations, with the exact nature of which we are 

 imperfectly acquainted, this class of substances is capable of 

 producing heat and of furnishing the carbonic acid elimi- 

 nated in respiration. The non-nitrogenized principles are 

 incapable in themselves of meeting the nutritive demands 

 of the system, and they are either consumed without form- 

 ing part of the tissues, or are deposited in the form of fat. 

 These questions we have already considered fully under the 

 head of alimentation ; and it will be remembered that, with 

 a few exceptions, fat always exists in the body uncombined, 

 either in the form of adipose tissue or fatty granulations in 

 the substance of other tissues. 



The non-nitrogenized elements taken up by the blood 

 may be divided into two varieties : one, the sugars, com- 

 posed of carbon with hydrogen and oxygen in the propor- 

 tions to form water, constituting the true hydro-carbons ; 

 and the other, the fats, in which the hydrogen and oxygen 

 do not exist in the proportion to form water. "We speak of 

 the sugars only, because starch and all varieties of sugar 

 taken as food are transformed into glucose. 



In connection with the study of proximate principles, ali- 

 mentation, and glycogenesis, we have already referred to the 

 destination of the true hydro-carbons in the organism. They 

 are taken as food to a considerable extent, particularly in the 

 form of starch, and are formed constantly by the liver, in all 



