78 GENERAL VIEW OF THE FUNCTIONS. 



sions a separation of its elements into those adapted for nutrition, and those of 

 which the character is excrementitious ; and this separation can scarcely be 

 regarded in any other light than as a chemical precipitation. The nutritious 

 portion is then taken up by the Absorbent vessels, or Lacteals, which are dis- 

 tributed on the walls of the alimentary canal ; whilst the remainder is propelled 

 along the intestinal tube by the simple contractility of its walls, undergoing at 

 the same time some further change, by which the nutritive materials are still 

 more completely extracted from it. And at last, the excrementitious matter, 

 consisting not only of a portion of the food taken into the stomach, but also of 

 part of the secretion of the liver, and of that of the mucous surface of the 

 intestines, is voided from the opposite extremity of the canal, by a muscular 

 exertion, which is partly reflex, like that of deglutition, but is partly voluntary, 

 especially (as it would appear) in Man. 



86. There seems no doubt that fluid, containing saline or other soluble 

 matters, may be absorbed by the blood-vessels, with which the mucous mem- 

 brane of the alimentary canal is so copiously supplied ; and this simple process 

 of Imbibition probably takes place, according to the physical laws of Endos- 

 mose. But the Selection and Absorption of the nutritious fluid appear to be 

 performed, not by vessels, but by cells ; which are developed at the extremities 

 of the villi, from germs previously existing there ; and which, after having 

 filled themselves with the ingredients drawn from the cavity of the intestinal 

 canal, deliver these to the lacteal absorbents, either by bursting, or by dissolv- 

 ftig away, their own term of life being expired. The absorbed fluid, which 

 now receives the name of Chyle, is propelled through the Lacteals by the 

 contractility of their walls ; aided in part, perhaps, by a vis a tergo derived 

 from the force of the absorption itself. With the reception of the nutritious 

 fluid into the absorbent vessels, commences its real preparation for organiza- 

 tion. Up to that period, it cannot be said to be in any degree vitalized ; the 

 changes which it has undergone being only of a chemical and physical nature, 

 and such as merely prepare it for subsequent assimilation. But in its passage 

 through the long and tortuous system of absorbent vessels and glands, it un- 

 dergoes changes which, Avith little chemical difference, manifest themselves 

 by a decided alteration in its properties ; so that the chyle of the thoracic duct is 

 evidently a very different fluid from the chyle of the lacteals, approaching much 

 nearer to blood in its general characters. These characters are such as indi- 

 cate that the process of organization and vitalization has commenced ; as may 

 be known alike from the microscopic appearance of the fluid, and from the 

 actions it performs when removed from the body. There is reason to believe 

 that the changes, which the Chyle undergoes in its progress through the lac- 

 teals, are due to the action of certain cells which are seen to be diffused through 

 the liquid ; these, by their own independent powers of growth, are continually 

 absorbing into themselves the fluid in which they float ; whilst, by bursting or 

 liquefying, as soon as their term of life is completed, they give this back in an 

 altered state. The Chyle thus modified is conveyed into the Sanguiferous 

 system of vessels, and flows directly to the heart ; by which it is transmitted, 

 with the mass of the blood, to the lungs. It there has the opportunity of ex- 

 creting 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 pabulum vitas for the whole system. 



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

 is destined to support, is a process evidently necessary for the conveyance to 

 them of the nutritious materials, which are provided for the repair of their 

 waste ; and for the removal of 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 ; 



