564- Proceedings of the British Association. 



beer, wine, spirits. These are Prof. Liebig's general principles of 

 nutrition. The second part of the work consists of details, in which 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 conclusions to which he has arrived on these subjects 

 are of such great and startling interest, that Dr. Playfair said, he dared 

 not venture to make an abstract of them, without entering into the calcu- 

 lations with which they were accompanied in the Professor's explanatory 

 remarks on digestion, he ascribes a singular function to saliva. 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, accompanies the food into the stomach, and there its oxygen 

 enters into combination with the constituents of the food, whilst its 

 nitrogen is again given out through the lungs or skin. The longer diges- 

 tion continues, the greater is the quantity of saliva, and consequently 

 of air, which enters the stomach. Rumination, in certain graminivor- 

 ous animals, has plainly for one object a renewed and repeated intro- 

 duction of oxygen. The Professor further touches upon the use of tea 

 and coffee as an article of food. Recent chemical research has proved, 

 that the active principles of tea and coffee — viz. teine and caffeine — are 

 absolutely one and the same body, perfectly identical in every respect. 

 The action of tea and coffee on the system must be therefore the same. 

 How is it that the practice of taking them has become necessary 

 to whole nations 1 Caffeine (teine) is a highly nitrogenized body. Bile, 

 as is well known, contains an essential nitrogenized ingredient — 

 taurine. Now, Prof. Liebig considers, that caffeine goes to the produc- 

 tion of this taurine ; and if an infusion of tea contains only one-tenth of 

 a grain of caffeine, still if it contribute, in point of fact, to the formation 

 of bile, the action even of such a quantity cannot be looked upon as 

 a nullity. Neither can it be denied, that, in case of using an excess 

 of non-azotized food, or deficiency of motion, which is required to 

 cause the change of matter in the tissues, and thus to yield nitrogenized 

 matter of the bile, that in such a condition the state of health may 

 be benefited by the use of tea or coffee, by which may be furnish- 

 ed the nitrogenized product produced in the healthy state of the 

 body, and essential to the production of an important element of respira- 

 tion. The American Indian, with his present habits of living solely 

 on flesh, could not with any comfort use tea as an article of food ; 

 for his tissues waste with such rapidity that, on the contrary, he has 

 to take something to retard this waste. And it is worthy of remark, 

 that he has discovered in tobacco smoke a means of retarding the 



