366 GENERAL VIEW OF THE HUMAN FUNCTIONS. 



are such as indicate that the process of organization and vitalization has com- 

 menced ; as may be known alike from the microscopic appearance of the fluid, 

 and from the actions it performs when removed from the body. The Chyle 

 thus modified is conveyed into the Sanguiferous system of vessels, and flows di- 

 rectly to the heart; by which it is transmitted, with the mass of the blood, to 

 the lungs. It there has the opportunity of excreting its superfluous carbonic 

 acid, and of absorbing oxygen; and probably acquires gradually the properties 

 by which the blood previously formed is distinguished, thus becoming the pabu- 

 lum vitde for the whole system. The fluid which is brought by the Lymphatic 

 system, from those parts of the organism to which it is distributed, is obviously 

 of a character no less nutritive than the chyle, though formerly regarded as ex- 

 crementitious; its source appears to be partly in the serous transudation which 

 escapes from the bloodvessels into the substance of the tissues, the superfluity 

 of which is taken up again and carried back into the circulation by the lympha- 

 tics; and partly, it may be, in the re-solution of such portions of the tissues 

 themselves, as, though dead, are not in a state of decomposition that prevents 

 their components from being again made available as nutritive materials. The 

 Lymph, like the chyle, seems to undergo an elaborating process in its passage 

 towards the thoracic duct, whereby it is gradually assimilated to blood in its 

 nature. 



380. The Circulation of the Blood through the tissues and organs which it is 

 destined to support, is a process evidently necessary, alike for supplying them 

 with the nutritious materials which are provided for the repair of their waste, 

 and for removing those elements of their fabric which are in a state of incipient 

 decomposition. In the lowest classes of organized beings, every portion of the 

 structure is in direct relation with its nutritive materials; it can absorb for itself 

 that which is required; and it can readily part with that of which it is desirable 

 to get rid. Hence, in such, no general circulation is necessary. In Man, on 

 the other hand, the digestive cavity occupies so small a portion of the body, that 

 the organs at a distance from it have no other means than their vascular com- 

 munication affords, of participating in the results of its operations; and it is, 

 moreover, necessary, that they should be continually furnished with the organi- 

 zable materials, of which the occasional operation of the digestive process would 

 otherwise afford only an intermitting supply. This is especially the case, as 

 already mentioned, with the Nervous system, which is so predominant a feature 

 in the constitution of Man; and we accordingly find both objects provided for, 

 in the formation of a large quantity of a semi-organized product, which contains 

 within itself the materials of all the tissues, and is constantly being carried into 

 relation with them. The propulsion of the Blood through the large trunks, 

 which subsequently divide into capillary vessels, is due to the contractions of a 

 hollow muscular organ, the Heart; but these, like the peristaltic movements of 

 the alimentary canal, are quite independent of the agency of the Nervous system ; 

 and are therefore to be referred to the class of Organic movements, such as occur 

 in Vegetables. The rate and force of the Heart's movements are greatly influ- 

 enced, however, by conditions of the Nervous system ; and these also, by calling 

 into play the contractility of the walls of the Arteries, exert a powerful influence 

 upon their caliber, and consequently upon the distribution of blood to particular 

 parts and organs, as we see in the acts of blushing and erection. 



381. Upon the circulation of the blood through all parts of the fabric, depends 

 in the- first place the Nutrition of the tissues. Upon this subject, formerly involved 

 in the greatest obscurity, much light has recently been thrown by Microscopic 

 discovery; it being now understood (as explained in the preceding Chapter), that 

 the continued growth and renewal of each tissue is effected by a continuation of 

 a process essentially similar to that by which it was first developed. The greatest 

 difficulty, in the present condition of our knowledge, is to comprehend the rea- 



