402 CHYLE. [Book ii. 



to be increased in passing through the lymphatic glands. It 

 has also been stated that the lymph in the finer lymph-vessels 

 clots even less firmly than that in the thoracic duct. From 

 tli is we may infer that some of the leucocytes in the adenoid 

 tissue of the follicles of a lymphatic gland find their way into 

 the lymph-sinus, and so into the efferent lymphatics, and that 

 some of the fibrin factors are added to the lymph, or at least 

 that some changes favourable to clotting are brought about. 



§ 240. We said that the large serous cavities of the peri- 

 toneum, pericardium, &c, are to be considered as parts of the 

 lymphatic system ; indeed pericardial or other serous fluid has 

 all the general characters of lymph. We have already said, 

 § 20, that these fluids when taken fresh from the body, clot 

 (this is, at least, the case in most animals) ; the clot when 

 examined microscopically is found to consist of colourless cor- 

 puscles like those of lymph or of blood entangled in the meshes 

 of fibrin. Both in their proteid and other chemical constitu- 

 ents these serous fluids resemble lymph. Analyses of the ac- 

 cumulations of fluid occasionally occurring in these cavities 

 shew that they contain sometimes less and sometimes more 

 solid matter than ordinary lymph. The aqueous humour of 

 the eye contains very little solid matter; and the cerebro- 

 spinal fluid is so peculiar that it had better be considered by 

 itself in connection with the nervous system. 



§ 241. Chyle. In fasting animals the fluid flowing along 

 the lacteals, as may be seen by inspection of the mesentery, is 

 clear and transparent ; it is lymph, differing, as we have said, 

 in no essential respects from the lymph flowing along other 

 lymphatic vessels. Shortly after a meal containing fat (and 

 every meal does contain some fat), the lymph becomes white 

 and opaque like milk, the more so the richer the meal is in fat ; 

 it is then called chyle. Owing to the relatively large quantity 

 of this milky fluid which for some time after a meal continues 

 to be poured into the thoracic duct, the contents of that duct 

 also become milky, and are also called chyle. In the thoracic 

 duct the chyle of the lacteals is more or less mixed with lymph 

 from other lymphatic vessels, but the former is so preponderat- 

 ing that the contents of the duct may be taken as illustrating 

 the nature of chyle. 



Chyle differs from lymph in one important respect, and one 

 only ; whereas lymph ordinarily contains a small quantity only 

 of fat, chyle contains a very large amount. The actual amount 

 of fat present in the chyle of the thoracic duct varies, as may 

 be expected, very considerably, according to the nature of the 

 meal, the stage of digestion, and various circumstances. Five 

 per cent, is a very common amount ; in the dog it has been 

 found to vary from 2 to 15 per cent. The increase in fat is 

 chiefly if not exclusively due to an increase in the neutral fats ; 



