66 INTRODUCTION. 



it is never discharged from the body in health. We have 

 already alluded to the view that the sugars and fats are 

 respiratory or calorific elements, which undergo oxidation 

 in respiration, and are immediately concerned in the produc- 

 tion of animal heat. One of the arguments in favor of this 

 function of fat has been that in cold climates, where there is 

 a greater demand for the generation of heat by the system, 

 fat is a more common and more abundant article of diet. 

 This is undoubtedly true, but other principles are consumed 

 in greater quantity, and the general process of nutrition, of 

 which the production of heat is but a single phenomenon, is 

 intensified. There is not sufficient ground for supposing that 

 fat has any such exclusive function. Its office is connected 

 with the general process of nutrition ; and its various trans- 

 formations in connection with this function, we have as yet 

 been unable to follow. 



Fatty Acids and Soaps. In addition to the fatty sub- 

 stances just described, the following fatty acids, free, and 

 united with bases to form soaps, have been found in the blood : 



Oleic Acid (C 36 H 33 O 3 HO), 

 Margaric Acid (C 34 H 33 O 3 HO) 



Oleate of Soda, 

 Mar gar ate of Soda. 



Oleic and margaric acids have been detected in minute 

 quantities in a free state in the blood and bile. Their 

 function is unknown. The oleate and margarate of soda are 

 found in small quantity in the blood, bile, and lymph. They 

 serve 'to hold in solution the small quantity of the fatty acids 

 and fats which exists in these fluids. The function of all 

 these substances is comparatively unimportant. In the blood 

 of the ox, Robin and Yerdeil have found a small quantity of 

 stearic acid and the stearate of soda. 



Odorous Principles. It is well known that the perspira- 



