50 REPORT — 1842. 



The other ingredients of food being fitted to sustain the temperature of the 

 body, he calls the elements of respiration. They are, 



Fat. Sugar of milk. 



Starch. Pectine. 



Gum. Bassorine. 



Cane-sugar. Wine. 



Grape-sugar. Beer. 



Spirits. 

 Having been led to give at such length an account of Professor Liebig's 

 general principles of nutrition, we must dismiss with a mere announcement 

 the details of which the second part of his work consist. In this he examines 

 the chemical processes engaged in the production of bile, of urea, uric acid 

 and its compounds, as well as of cerebral and nervous substance. The con- 

 clusions to which he has arrived on these subjects are of the most intense in- 

 terest, and have surprised their author as much as they must his reader. In 

 fact, we dare not venture to make an abstract of them, without entering into 

 the calculations with which they are accompanied,, lest their beautiful har- 

 mony with known operations would incline the reader to think that they are 

 the creations of a brilliant imagination, instead of being (as they are) the re- 

 sults of sober calculation. 



His explanatory remarks on digestion are highly beautiful, and we cannot 

 pass them without referring to the singular function which he ascribes to 

 saliva. 



In the action of gastric juice on the food, no other element participates 

 except the oxygen of the atmosphere and the elements of water. During 

 the mastication of food the fluid saliva is secreted into the mouth. This fluid 

 possesses the remarkable property of enclosing air in the shape of froth, in a 

 far higher degree even than soap-suds. This air, by means of the saliva, ac- 

 companies the food into the stomach, and there its oxygen enters into combi- 

 nation with the constituents of the food, whilst its nitrogen is again given 

 out through the lungs or skin. This, then, accounts for the fact discovered 

 by physiologists, that pure nitrogen is given out by the lungs and skin. The 

 greater the resistance of the food, that is, the longer digestion continues, the 

 greater is the quantity of saliva, and consequently of air, which enters the 

 stomach. Rumination, in certain graminivorous animals, has plainly for one 

 object a renewed and repeated introduction of oxygen ; for a. mere mechani- 

 cal division of the food only shortens the time required for solution. Of 

 course, the Professor does not mean to infer that this is the only mode by 

 which oxygen enters the stomach ; it does so also by the property possessed 

 by all animal tissues of being permeable to air. 



The Professor, in treating of the formation of bile, shows the very inter- 

 esting result, that if the formula of the compounds existing in urine and 

 those of the bile be added together, we obtain the precise formula of the 

 blood ; as was indeed to be expected from his view, that the nitrogenous 

 matters go principally to the former fluid, the carbonaceous matters to the 

 latter. He enters largely into the hitherto mysterious transformations of 

 bile into choleic acid, taurine, &c. ; and as a consequence of this examination 

 he obtains the remarkable result, that if the elements of prcteine and starch 

 (oxygen and water being also present) undergo transformation together and 

 mutually affect each other, Ave obtain, as the products of this metamorphosis, 

 urea, choleic acid, ammonia and carbonic acid, and besides these no products 

 whatever ! This is full of significance with regard to the processes which 

 we actually know to proceed in the animal ceconomy. 



Following out the subject still further, he accounts very happily for the 



