260 ADIPOSE TISSUE. [BOOK I. 



of capillaries. They develope with special frequency in areolar tissue, 

 especially in the subcutaneous areolar tissue and in the connective 

 tissue which lies around and bet ween certain of the abdominal viscera. 

 In certain situations (as e.g. in the orbit) the areolar tissue is never 

 free from fat ; in other situations, as in the subcutaneous connective 

 tissue of the eyelids, of the penis, and scrotum, fat cells are never 

 present. 



The fully formed fat cell presents 'the appearance of a little bag 

 distended with glistening oily contents, and with no appearance of a 

 nucleus or of typical protoplasm. In reality, however, it can be 

 shewn that even the fully formed fat cell contains a nucleus 

 with remains of the original cell protoplasm around it, though these 

 are so pressed upon and surrounded as to be invisible until some 

 cause comes into operation to remove a part at least of the oily 

 contents. 



The contents of the fat cells are during life of flu id consistence and 

 only solidify when the tissue containing them is cooled below 25 C. 

 When solidifying, the oily matter often separates, at least in part, 

 in the form of groups of needles ; sometimes in small single needles. 



When adipose tissue is treated with ether, this fluid extracts and 

 dissolves more or less completely the fatty contents of the cells, in 

 which the remains of the nucleus and protoplasm may be then 

 detected. 



The wall of the fat cell is not acted upon by acetic acid nor by 

 dilute mineral acids; it is easily dissolved by natural or artificial 

 gastric juice. When treated with a solution of perosmic acid, the 

 fatty matter contained in fat cells is stained of an intense black 

 colour ; this reagent is admirably adapted for the microchemical detec- 

 tion of fatty bodies. 



In this section a description will be given of the principal constituents 

 of the adipose tissue of man and the higher animals, the discussion of the 

 origin of fat in the economy being postponed to that division of this work 

 in which certain general chemical processes of the body are treated of 

 under the heading of Nutrition. A consideration of the fatty matters which 

 occur in particular organs or fluids (as for instance in the nervous organs and 

 in milk) is given in the chapters devoted to these subjects. 



Mode of ex- The fatty matters which are contained in adipose 



tracting the tissue are best extracted by drying the tissue so as to 

 fats of adipose expel the water which it contains, and then boiling the 

 finely divided or comminuted tissue in ether, which 

 dissolves all the fats. The etheral solution is then evaporated to 

 dryness. The residue contains the fats, mixed with small quantities 

 of other bodies soluble in ether, such as cholesterin and lecithin. 



In some cases the fatty matters of adipose tissue can be separated 

 in large quantities by the combined action of heat (which causes the 

 fats to melt) and pressure ; or by boiling the tissue with water, when 

 the melted oil floats to the surface and can be skimmed off. These 



