278 



THE MICROSCOPE AND ITS REVELATIONS. 



nearly spherical or spheroidal form; sometimes, however? when they are 

 closely pressed together, they become somewhat polyhedral, from the 

 flattening of their walls against each other (Fig. 468). Their intervals 

 are traversed by a minute network of blood-vessels (Fig. 480), from 

 which they derive their secretion; and it is probably by the constant 

 moistening of their walls with a watery fluid, that their contents are 

 retained without the least transudation, although these are quite fluid at 

 the temperature of the living body. Fat-cells, when filled with their 

 characteristic contents, have the peculiar appearance which has been 

 already described as appertaining to oil-globules ( 154), being very 

 bright in their centre, and very dark towards their margin, in conse- 

 quence of their high refractive power; but if, as often happens in prepa- 

 rations that have been long mounted, the oily contents should have 

 escaped, they then look like any other cells of the same form. Although 

 the fatty matter which fills these cells (consisting of a solution of 

 Stearine or Margarine in Oleine) is liquid at the ordinary temperature 



FIG. 468. 



FIG. 469. 



Areolar and Adipose tissue; a, 

 a, fat-cells; &, b, fibres of areolar 

 tissue. 



Cellular Cartilage of Mouse's ear. 



of the body of a warm-blooded animal, yet its harder portion sometimes 

 crystallizes on cooling; the crystals shooting from a centre, so as to form 

 a star-shaped cluster. In examining the structure of Adipose tissue, it 

 is desirable, where practicable, to have recourse to some specimen in 

 which the fat-cells lie in single layers, and in which they can be 

 observed without disturbing or laying them open; such a condition is 

 found, for example, in the mesentery of the Mouse; and it is also occa- 

 sionally met with in the fat-deposits which present themselves at inter- 

 vals in the connective tissues of the muscles, joints, etc. Small collec- 

 tions of fat-cells exist in the deeper layers of the true skin, and are 

 brought into view by vertical sections of it (Fig. 463, /). And the 

 structure of large masses of fat may be examined by thin sections, these 

 being placed under water in thin cells, so as to take-off the pressure of 

 the glass-cover from their surface, which would cause the escape of the 

 oil-particles. No method of mounting (so far as the Author is aware) is 

 successful in causing these cells permanently to retain their contents. 



675. Cartilage. In the ordinary forms of Cartilage, also, we have an 

 example of a tissue essentially composed of cells; but these are commonly 



