SECRETION. 



441 



individual. The lamtgo of the human foetus 

 is an homologous production, and must, I 

 think, similarly serve in its economy, by re- 

 moving from the blood, as so much excreted 

 matter, the materials of which it is composed. 

 " Now if this be reasonable, we may carry 

 this principle to the apprehension of the true 

 import of the hair, which exists in a kind of 

 rudimental state on the general surface of our 

 bodies, and to that of many other permanently 

 rudimental organs, such as the mammary 

 glands of the male and others. For these 

 rudimental organs certainly do not serve, in a 

 lower degree, the same purposes as are served 

 by the homologous parts which are completely 

 developed in other species, or in the other 

 sex. To say they are useless, is contrary to 

 all we know of the absolute perfection and 

 all-pervading purpose of creation ; to say they 

 exist merely for the sake of conformity with 

 a general type of structure, is surely unphilo- 

 sophical ; for the law of unity of organic types 

 is, in larger instances, not observed, except 

 when its observance contributes to the advan- 

 tage of the individual. No ; all these rudi- 

 mental organs must, as they grow, be excre- 

 tions serving a definite purpose in the economy 

 by removing their appropriate materials from 

 the blood, and leaving it fitter for the nutrition 

 of other parts, or adjusting the balance which 

 might else be disturbed by the formation of 

 some other part. Thus they minister to the 

 self-interest of the individual ; while, as if for 

 the sake of wonder, beauty, and perfect order, 

 they are conformed with the great law of 

 unity of organic types, and concur with the 

 universal plan observed in the construction of 

 organic beings." 



We cannot have a better example of the 

 close affinity between the functions of nutri- 

 tion and secretion, in regard alike to their 

 essential nature and to their purpose, than 

 that which is afforded by the structure, 

 growth, and offices of the adipose tissue. 

 Fat, wherever it exists, whether in large 

 isolated masses, or dispersed through areolar 

 tissue, is made up of an aggregation of minute 

 cells, whose peculiar province it is to draw 

 into themselves the superfluous oleaginous 

 matter of the blood, as a part of the history 

 of their own development. Since they form 

 constituent parts of the organism, and may 

 possess as great a duration as that of any 

 other of the elements of the soft tissues of 

 the body, the growth of fat cells is commonly 

 regarded as an act of nutrition. But it may 

 also be considered as an act of secretion ; for 

 it is the means of separating from the blood a 

 product which is not destined to undergo any 

 further organisation, and whose accumulation 

 in the circulating fluid, beyond a very small 

 and limited amount, would be positively 

 noxious. This very same act of elimination 

 of fatty matter, when performed by the cells 

 of the liver, or of the sebaceous follicles of the 

 skin, or (abnormally) by those of the kidney 

 or of the intestinal glandulae, is recognised as 

 forming part of the function of excretion, the 

 difference being simply in the position and re- 



lations of the secreting cells. For whilst 

 those of the glands are placed upon or near 

 the free surfaces of follicles or ducts, and are 

 destined from the first to a speedy exuviation, 

 those of fat are woven up with areolar fibres 

 and membranes, and form solid masses of 

 tissue. A distinction might be drawn, on the 

 ground that the contents of the fat cells are 

 destined to be again taken into the circula- 

 tion ; whilst those of glandular cells, having 

 been once eliminated from the blood, are 

 never to return to it. But this would not hold 

 good ; for the fat cells appear to have an in- 

 definite duration, the reception of their con- 

 tents into the circulating current seeming 

 entirely to depend upon the demand for these 

 in the blood* ; and there is now sufficient 

 evidence that a considerable part of the bile 

 that has been secreted and poured into the 

 intestinal canal is destined for re-absorption. 

 And if we admit that the spleen, thymus 

 and thyroid bodies, and supra-renal capsules, 

 are to be regarded as possessing a glandular 

 character, although the products of their 

 elaboration are destined to be received back 

 again into the current of the circulation, it is 

 difficult to find a reason for the exclusion of 

 a mass of adipose tissue from the same 

 category. 



Of the organs of secretion. In order that 

 we may duly understand the real nature of 

 the secreting process, as elucidated by recent 

 discoveries, it is requisite that we should ex- 

 amine into the nature of the instruments by 

 which it is effected. There can scarcely be 

 a more beautiful illustration of the doctrine 

 that physiology is as capable as any other 

 science of being reduced to general prin- 

 ciples, and that these principles must, if 

 valid, be of universal operation, than the fact 

 that the process of secretion common as it 

 is in all its essential features to the animal 

 and vegetable kingdoms is every where per- 

 formed by the same agency, namely, the de- 

 velopment of simple cells, each possessing its 

 own independent vitality ; these bodies form- 

 ing the really operative part of every secreting 



* May not this re-entrance be governed simply 

 by physical laws ? There can be no question that 

 the chief purpose of fat is to serve as a store of 

 combustible matter, for the maintenance of the heat 

 of the body, when there is a deficiency of materials 

 in the blood. A certain proportion of fatty matter 

 (from 4 to 6 parts in 1000) seems normally to exist 

 in the blood ; and this is usually renewed from the 

 food as rapidly as it is eliminated by the respiratory 

 process, or by the nutrition of the nervous tissue. 

 But if the supply be withheld, a diminution of the 

 quantity of oleaginous matter in the circulating 

 current must rapidly take place ; and it is then that 

 we find the contents of the fat-cells reabsorbed into 

 the blood. It has been shown by Matteucci that 

 oleaginous matter will pass through a membranous 

 septum towards a slightly alkaline fluid, such as the 

 blood ; and it does not seem difficult to understand, 

 therefore, how the fat-cells should give up a portion 

 of their contents when the alkalinity of the blood is 

 no longer neutralised by the fatty matter which it 

 normally contains, and how just that amount should 

 pass back again, which is necessary to keep up the 

 due proportion of fatty matter in the blood, and no 

 more. 



