Organs of Respiration and Circulation. 



573 



differing- in density are separated by a thin animal or vegetable 

 membrane, there is a tendency to mutual admixture through the 

 pores of the membrane ; but the less dense fluid will transude 

 Avith much greater facility than the more dense: and consequently 

 there will be an increase on the side of the denser fluid ; whilst 

 very little of this, in comparison, will have passed towards the less 

 dense. When one of the fluids is contained in a sac or cavity, 

 the flow of the other towards it is termed Endosmose, or flow- 

 inwards ; whilst the contrary current is termed Exosmose, or 

 flow-ouhvards, Thus, if the caecum of a fowl filled with syrup 

 or gum-water be tied to the end of a tube, and be immersed in 

 pure water, the latter will penetrate the caecum by endosmose, 

 and will so increase the volume of its contents as to cause the 

 fluid to rise to a considerable height in the attached tube. On 

 the other hand, a small proportion of the gum or syrup will find 

 its way into the surrounding fluid by exosmose. But if the 

 caecum were filled with water, and were immersed in a solution 

 of gum or syrup, it would soon be nearly emptied, — the exosmose 

 being much stronger than the endosmose." * 



The chyle, by the operation of this law being conveyed into the 

 lacteals, is carried by them into a receptacle marked c in fig. 2, 

 situated near to the lumbar vertebrae, and in its course it passes 

 through the mesenteric glands, where it is further elaborated and 

 fitted for its conversion into blood. For the purpose of making 

 this better understood, it is necessary to state that the intestines 

 are attached to the spine, by a double reflection of the serous 

 membrane which lines the abdomen, termed the mesentery, and 

 that the lacteals travel upon this to reach the receptaculurn cliyli. 

 These several parts are depicted in fig. 2, where the lacteals are 

 marked a, the mesenteric glands 5, and the chyle-receptacle c. 



To enter into a description of the particular changes which are 

 wrought in the chyle by passing through the mesenteric glands 

 would encroach too much on the subject of this lecture, and it 

 will be sufficient to observe that, quitting the glands, it is found 

 to contain a large number of spherical corpuscules, and to possess 

 a power of clotting, like the fibrine of the blood. These corpus- 

 cules are formed from the lining membrane of the chyle-convey- 

 ing tubes ; they average in size about the 4600th of an inch, and 

 are probably identical with the white corpuscules of the blood, 

 as these latter are well known to be chiefly concerned in nutrition. 

 The lacteals form frequent unions with each other, by which their 

 size is increased, but their number diminished, so that they ulti- 

 mately enter the receptacle by a very few trunks. (See fig. 2.) The 

 mesenteric glands are composed of coils of these tubes, ramifying 



* Carpenter^ 'Manual of Physiology,' p. 28i. 



