Chemical Physiology and Pathology. 531 



brought into use for the purpose of combustion. The for- 

 mation of fat is thus dependent on a deficiency of oxygen, 

 which is absolutely essential to the disengagement of car- 

 bon. — In closest connection with the process of respiration 

 and the production of fat, stands (according to Liebig) the 

 secretion of bile. The bile which is loaded with carbon, 

 is removed only in very small quantities along with the ex- 

 crement, and its greater portion returns into the circulation, 

 becomes carbonic acid by combustion, develops heat, and is 

 in fine removed from the body by the process of respiration. 

 It may be borne in mind, that Mulder and Liebig disagree 

 as to the manner in which oxygen is taken up by the blood, 

 also that some chemists (as Kemp) deny in toto that either 



bile or fat is employed in respiration. In accordance 



with the foregoing views, articles of food are (by Liebig) 

 divided into those which contain, and those which are free 

 from, nitrogen. To the first, or plastic ones as they are called, 

 belong all those which contain the proteine, in the form of 

 albumen, fibrine or caseine, and not in an already metamor- 

 phosed state, from which it is no longer reducible. Liebig 

 names these substances which are free from nitrogen, respira- 

 tory-nourishing, because they supply to carbon the materials 

 for breathing and the production of heat. All these sub- 

 stances are converted in the stomach, with the aid of the 

 gastric juice, (consisting of pepsine and weak mineral acids) of 

 water, and the oxygen of the air swallowed, into a condition in 

 which they are fitted for passing into the blood. Pepsine, is 

 a body found in a peculiar state of transformation, and causes 

 (like yeast in fermentation) by contact with the portions of 

 food which are insoluble in water, a new grouping of their 

 elements, (perhaps to be named albuminous fermentation). A 

 certain quantity of pepsine can probably only dissolve a certain 

 quantity of food, just as so much yeast converts into alcohol 

 and carbonic acid only so much sugar. The mineral acids of 

 the gastric juice, without which the pepsine does not act, 



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