Ixviii ADIPOSE TISSUE. 



Accordingly it has been observed that, unless when such traversing nervous 

 twigs happen to be encountered, a puncturing instrument may be carried 

 through the adipose tissue without occasioning pain. 



As to the uses of the fatty tissue, it may be observed, in the first place, that it 

 serves the merely mechanical purpose of a light, soft, and elastic packing material 

 to fill vacuities in the body. Being thus deposited between and around different 

 organs, it affords them support, facilitates motion, and protects them from the inju- 

 rious effects of pressure. In this way, too, it gives to the exterior of the body its 

 smooth, rounded contour. Further, being a bad conductor of heat, the subcutaneous 

 fat must so far serve as a means of retaining the warmth of the body, especially 

 in warm-blooded creatures exposed to great external cold, as the whale and other 

 cetaceous animals, in which it forms a very thick stratum, and must prove a much 

 more effectual protection than a covering of fur in a watery element. 



But the most important use of the fat is in the process of nutrition. Composed 

 chiefly of carbon and hydrogen, it is absorbed into the blood and consumed in respi- 

 ration, combining with oxygen to form carbonic acid and water, and thus contributing 

 with other hydrocarbonous matters to maintain the heat of the body ; and it is sup- 

 posed that when the digestive process introduces into the system more carbon and 

 hydrogen than is required for immediate consumption, the excess of those elements 

 is stored up in the form of fat, to become available for use when the expenditure 

 exceeds the immediate supply. According to this view, active muscular exercise, 

 which increases the respiration, tends to prevent the accumulation of fat by increasing 

 the consumption of the hydrocarbonous matter introduced into the body. Again, 

 when the direct supply of calorific matter for respiration is diminished or cut off by 

 withholding food, or by interruption of the digestive process, nature has recourse to 

 that which has been reserved in the form of fat ; and in the wasting of the body 

 caused by starvation, the fat is the part first consumed. 



The use of the fat in nutrition is well illustrated by what occurs in the hedgehog 

 and some other hybernating animals. In these the function of alimentation is sus- 

 pended during their winter-sleep ; and though their respiration is reduced to the 

 lowest amount compatible with life, and their temperature falls, there is yet a con- 

 siderable amount of hydrocarbonous material provided in the shape of fat, before 

 their hybernation commences, to be slowly consumed during that period, or per- 

 haps to afford an immediate supply on their respiration becoming again active in 

 spring. 



It has been estimated that the mean quantity of fat in the human subject is 

 about one-twentieth of the weight of the body, but from what has been said, it is 

 plain that the amount must be subject to great fluctuation. The proportion is 

 usually largest about the middle period of life, and greatly diminishes in old age. 

 High feeding, repose of mind and body, and much sleep, favour the production of 

 fat. To these causes must be added individual and perhaps hereditary predispo- 

 sition. There is a greater tendency to fatness in females than males ; also, it is said, 

 in eunuchs. The effect of castration in promoting the fattening of domestic animals 

 is well known. 



In infancy and childhood the fat is confined chiefly to the subcutaneous tissue. 

 In after-life it is more equally distributed through the body, and in proportionately 

 greater quantity about the viscera. In Hottentot females fat accumulates over the 

 gluteal muscles, forming a considerable prominence; and, in a less degree, over the 

 deltoid. A tendency to local accumulations of the subcutaneous fat is known to 

 exist also in particular races of quadrupeds. 



Development. According to Valentin, the fat first appears in the human 

 embryo about the fourteenth week of intra-uterine life. At this period fat 

 is deposited in cells already formed in the tissues. The cells first seen are 

 for the most part insulated, but by the end of the fifth mouth they are col- 

 lected into small groups. They are also at first of comparatively small size. 

 As already stated, the foetal fat- cells in their early condition contain a 

 nucleus which is afterwards hidden from view. 



