Nitrogen contained in Alimentary Substances. 351 



of alimentary bodies, has in an equal degree represented the 

 essential differences in their chemical composition and their 

 physiological effects, or has presented to the eye of the mind 

 the important part which these substances perform, as the 

 above-mentioned distinction, which is also identical with that 

 oi azotised and non-azotised bodies. 



In order to give some indication of the state of confusion 

 which existed, even in this most elementary proposition of 

 dietetics, previous to that distinction being made, it may not 

 be more than necessary to mention the idea of that classical 

 author, Dr. Prout*, that the nutritive power is in direct pro- 

 portion to the quantity of carbon. At the present day not a 

 single fact is known which can support the idea of the animal 

 body being able to form azotised from non-azotised substances, 

 — possibly, under the influence of ammonia or of nitrogen 

 from the atmosphere; on the contrary, all experiments, as 

 well as daily observation, seem to prove the absolute neces- 

 sity of azotised food for the preservation of the individual. 

 Chemistry has likewise demonstrated the presence of a more 

 or less high, but constant proportion of nitrogen in all the 

 tissues and fluids of the animal body, while in all those sub- 

 stances which, according to our modern ideas, are the most 

 nutritive, namely, the proteine compounds, the carbon is pre- 

 sent in medium quantity. Those substances esteemed by 

 Prout the most nourishing, because richest in carbon, as the 

 fats and oils, must be altogether excluded from the list of re- 

 productive bodies, except in so far as fatty matter is necessary 

 to the formation of animal cells. The chemical physiologist 

 could make use of the theory of Prout, in measuring the 

 fitness of the bodies necessary to respiration, if along with 

 the carbon could be taken into account the quantity of com- 

 bustible or unoxidized hydrogen contained in them ; but for 

 those substances, which in the strict sense of the word are ca- 

 pable of being transformed into blood and animal tissue, ac- 

 cording to our present knowledge, the capability for these 

 purposes may be estimated relatively by the amount of nitro- 

 gen. This has been already done to a certain extent by the 

 researches of several chemists and physiologists, but, so far as 

 we are aware, it has been confined to vegetables; and it there- 

 fore appeared to us not to be without interest to make use of 

 the same principle in extending the investigation to the various 

 alimentary substances taken from the animal kingdom, and so 

 to give to the physiologist a basis founded on facts in a de- 



* See Mayo's Outlines of Human Physiology, p. 206, second edition, 

 London, 1829. 



