I'AT. 61 



but forms no special envelope to the smaller clusters ; and although 

 fine fasciculi and filaments of that tissue pass irregularly over and 

 through the clusters, yet it is probable that the vesicles are held 

 together in these groups mainly by the fine network of capillary vessels 

 distributed to them. In the marrow the connective tissue is very 

 scanty ; indeed, the fat-cells in some parts of the bones are said to be 

 altogether unaccompanied by connective filaments. 



The adipose tissue is copiously supplied with blood-vessels. The 

 larger branches of these pass into the fat-lumps, where they run between 

 the lobules and subdivide, till at length a little artery and vein are sent 

 to each small lobule, dividing into a network of capillary vessels, which 

 not only surrounds the cluster externally, but passes through between 

 the vesicles in all directions, supporting and connecting them. The 

 lymphatics of the fat are in close relation to the blood-vessels, 

 accompanying and occasionally completely enclosing them, as they 

 enter the lobule. No nerves have been seen to terminate in this tissue, 

 although nerves destined for other textures may pass through it. 

 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. 



Uses and Amount. — As to the uses of the fatty tissue, it may be observed, in 

 the first place, that it serves the merely mechanical pui-pose 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 injurious effects of pressui-e. In this wa}% too, it 

 gives to the exterior of the body its smooth, rounded contoui". Fuilher, being a 

 bad conductor of heat, the subcutaneous fat must so far seiTe as a means of 

 retaining the warmth of the body, especially in wann-blooded creatures exposed 

 to great external cold, as the whale and other cetaceous animals, in which it 

 fomis a very thick stratum. 



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

 posed chiefly of carbon and hydrogen, it is absorbed into the blood and consumed 

 in respiration, combining with oxygen to fomi carbonic acid and water, and thus 

 contributing Avith other hydrocarbonous matters to . maintain the heat of the 

 body ; and it is supposed that when the digestive process introduces into the 

 system more carbon and hj-drogen than is requii'ed 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 tlie immediate supply. According to this 

 Anew, active muscular exercise, which increases the respiration, tends to prevent the 

 accumulation of fat by increasing the consumption of the hychocaibonous matter 

 introduced into the body. Again, when the direct supply of calorific matter for 

 respiration is diminished or cut off by AA'ithholding food, or by inteiTuption of the 

 digestive process, nature has recourse to that which has been reserved in the 

 fonn of fat ; and in the wasting of the body caused by starvation, the fat is the 

 part fii'st consumed. 



The use of the fat in nutrition is well illustrated by what occiu's in the hedge- 

 hog and some other hybernating animals. In these the function of alimentation 

 is suspended diuing their AA-inter sleep ; and though their respuvition is reduced 

 to the lowest amount comi^atible with life, and their temperatui-e falls, there is 

 yet a considerable amount of hydi-ocarbonous material provided in the shape of 

 fat, before theii- hybernation commences, to be slowly consumed during that 

 period, or perhaps to afford an immediate supply on then- respiration becoming 

 again active in spring. 



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

 about one-tw^entieth of the weight of the body, but from Avhat has been said, 

 it is plain that the amount must be subject to gi-eat fluctuation. The proportion 



