160 STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



that Animals usually elaborate them by any transforming process-from 

 the elements of their ordinary food.. The mode in which they are taken 

 into the blood, and the uses to which they are subservient, will be here- 

 after investigated : but it may be here remarked, that the portion sepa- 

 rated from the circulating fluid to form the Adipose tissue, is only that 

 which can be spared from the other purposes, to which the fatty matters 

 have to be applied. Hence the production of this tissue depends in part 

 upon the amount of Fatty matter taken in as food ; but this is not en- 

 tirely the case, as some have maintained ; for there is sufficient evidence 

 that animals may produce fatty matter by a process of chemical trans- 

 formation, from the starch or sugar of their food, when there is an un- 

 usual deficiency of it in their aliment. 



262. The development of Adipose tissue in the body appears to an- 

 swer several distinct purposes. It fills up interstices, and forms a kind 

 of pad or cushion for the support of moveable parts ; and so necessary 

 does it seem for this purpose, that, even in cases of great emaciation, 

 some fat is always found to remain, especially at the base of the heart 

 around the origin of the great vessels^ and in the orbit of the eye. It 

 also assists in the retention of the animal temperature by its non-con- 

 ducting power ; and we accordingly find a thick layer of it, in those 

 warm-blooded mammals that inhabit the seas, either immediately be- 

 neath their skin, or incorporated with its substance. Its most important 

 use, however, is to serve as a reservoir of combustible matter, at the 

 expense of which the respiration may be maintained when other mate- 

 rials are deficient; thus we find that the respiration of hybernating 

 animals is kept up, during the period when they cease taking food 

 ( 121), by the consumption of the store of fat which was laid up in 

 their bodies, previously to their passing into that state; and it is also 

 to be noticed that herbivorous animals, whose food is scanty during the 

 winter, usually exhibit a strong tendency to such an accumulation, 

 during the latter part of the summer, when their food is most rich and 

 abundant, in order to supply the increased demand created by the low 

 external temperature of the winter season. Other circumstances being 

 the same, it appears that the length of time during which a warm-blooded 

 animal can live without food, depends upon the quantity of fat in its 

 body; for the rapid lowering of its temperature, which is the immediate 

 cause of its death ( 117), takes place as soon as the whole of this store 

 has been exhausted. Of the means by which the fatty secretion is taken 

 back again into the current of the circulation, when it is required for 

 use in the system, we know nothing whatever. 



263. In order that it may be applied to the maintenance of the ani- 

 mal heat, the fatty matters must be received back into the blood ; and 

 although we have no certain knowledge of the mode in which this is 

 accomplished, yet it may be surmised to be as follows. The Blood nor- 

 mally contains a certain amount of fatty matter, held in solution by 

 combination with its alkali ; and should this be exhausted by the com- 

 bustive process, the circulating current will draw into itself a fresh sup- 

 ply from the interior of the fat-cells ; it having been shown by Mat- 

 teucci that oleaginous particles will pass through animal membranes by 



