568 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



these two propositions: (1) The part played by these several food-stuffs in the 

 total metabolism depends on the composition of the fluid feeding the cell. 

 The greater the amount of one of these food-stuffs, the greater its decompo- 

 sition and the less the decomposition of the others, so long as the total decom- 

 position sutlers no change. (2) The several food-stufls do not act wholly on 

 account of their quantity in the fluid surrounding the cell, but especially accord- 

 ing to the chemical affinity of the cell-substance for them individually. First 

 in this regard comes proteid, then carbohydrates, and lastly fat. 



The excessive proteid decomposition in diabetes is due to the non-combus- 

 tion of the proteid protecting sugars, 1 and the same is in part true in fever, 

 where a small supply of carbohydrates reaches the blood. 2 Dextrose and 

 levulose weight for weight have equal value in protecting proteid metabolism. 3 



For further discussion of carbohydrates in the body see under the indi- 

 vidual sugars, and under Fat in the Body. 



Benzol Derivatives or Aromatic Compounds. 

 The aromatic compounds are characterized by a configuration in which six 

 atoms of carbon are linked together in a circle called the benzol ring. The 

 type of this is benzol, a hydrocarbon found in coal-tar and having the formula, 



H 1 



H— C C— H 



H— C C— H 



\ // °\/' 



C 4 



H 



The hydrogen atoms may be substituted by others, substitution of one OH 



group, for example, forming phenol, C 6 H 5 — OH. If, however, two OH 



groups are substituted, three different bodies, corresponding to the different 



arrangements on the ring, become possible. If the two OH groups occupy 



the positions 1 and 2 the substance is ortho-dioxy benzol; if 1 and 3, meta- 



dioxybenzol ; and if 1 and 4, ^am-dioxybenzol. 



It is possible to convert bodies of the fatty series into those of the aro- 

 matic. Acetylene passed through red-hot tubes yields benzol. On the other 

 hand, aromatic bodies may be converted into those of the fatty series. If 

 phenol in aqueous solution be subjected to electrolysis by an alternating cur- 

 rent under which cireumstanccs hydrogen and oxygen are alternately liberated 

 on the same pole, the effect of this intermittent oxidation and reduction is to 

 break up the phenol into caproic acid, and finally, after passing through acids 

 of lower carbon contents, into carbonic acid and water. 



The aromatic compounds found in the urine are normally exclusively 



1 Lu-k : Zetischriftfur Biolopie, 1890, Bd. 27, S. 459. 2 May: Ibid., 1894, Bd. 30, S. 1. 



3 De Renzi mid Realis: VI I. Congress/iir innere Medizin, 1S96. 



