32 



PHYSIOLOGY. 



Fig. 7. 



This tissue is usually diffused over the whole body, either in the 

 areolar tissue, or in small clusters covered by the comnion envelope; 

 and even in cases of great emaciation there is some fat always left, 

 especially at the base of the heart, around the great vessels, &c. 

 Fat-cells are spherical or spheroidal ; when closely pressed to- 

 gether they assume a polyhedral form. 

 (Fig. 7.) Large masses of fat are often 

 formed by their aggregation, the com- 

 ponent parts being held together by 

 areolar tissue, and also by the blood- 

 vessels which ramify minutely among 

 them, forming a capillary network 

 upon the smallest lobules, and even 

 between the individual cells. This 

 \ if W"''i"fc,, / i \ '''I J tissue contains neither lymphatics nor 



nerves. 



The fat is contained in the interior 

 of these cells, where it is deposited from the blood-vessels. Its con- 

 sistence varies according to the proportion of the organic elements 

 entering into its composition. These are elaine or oleine, stearine, 

 and margarine ; the last two, which are solid when separated, being 

 dissolved in the former at the ordinary temperature of the body. 

 The oil thus formed in the interior of the cells is prevented from 

 escaping, by the moistening of the cell-walls by the watery fluid 

 circulating through the vessels. All the substances above named 

 are regarded by chemists as salts^ being compounds of the oleic, 

 stearic, and margaric acids with a base, called from its sweet taste, 

 glycerine. 



The fat is analogous to the starch of vegetables, and has a like 

 use, viz.: to supply elements of nutrition, when other sources are 

 cut off. It also answers the important purpose of retaining the 

 animal temperature by its non-conducting properties ; and the still 

 more important object of serving as a kind of reservoir of combusti- 

 ble matter against the time of need. Fat appears to be deposited 

 only when an excess of non-azotized alimentary matter is introduced 

 into the body, over and above the wants of the system. 



Cartilage in its simplest form consists merely of nucleated cells, 

 and greatly resembles the cellular tissue of plants. In other forms, 

 however, the cells are imbedded in an intercellular substance, or 

 matrix^ called cliondrine. This substance bears a strong resem- 

 blance to gelatine, but requires longer boiling in water to effect its 

 solution. It is not precipitated by tannic acid, but Z5, by acetic acid, 

 alum, acetate of lead and proto-sulphate of iron. It agrees more 

 nearly with the proteine compounds, in composition, than gelatine, 

 and may be considered as an intermediate stage between the two. 



Cartilage, in general terms, may be considered a non-vascular 

 substance, considerable masses of it existing unpenetrated by a single 



