THE NATURE AND MOVEMENTS OF LYMPH. 317 



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 preponderating 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 : where- 

 as 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 ; though whether the small quantity of soaps 

 and of lecithin present is greater than in lymph has not been distinctly as- 

 certained. Cholesterin is probably present in greater amount than in lymph, 

 since it probably comes from the bile poured into the intestines during diges- 

 tion ; but this is not certain. How far the nature of the fat, that is, the 

 proportion of the various kinds of fat, of stearin, etc., varies with the fats 

 present in the meal has not been definitely ascertained. 



The condition of the fat in chyle is peculiar. Some of it exists, like the 

 fat in milk, in the form of fat-globules of various sizes, but all small. A 

 very considerable quantity, however, is present in the form of exceedingly 

 minute spherules or granules, far smaller than any globules to be seen in 

 milk ; these exhibit active " Brownian movements." The fat present in this 

 form is spoken of as the " molecular basis " of chyle, and is very distinctive 

 of chyle. In the emulsified contents of the intestine, often called chyle, the 

 fat is finely divided, and to a large extent into small globules, but there is 

 nothing corresponding to this molecular basis ; the fat does not assume this 

 condition until it has passed out of the intestine into the lacteals. Lymph 

 examined with the microscope shows besides the white corpuscles only very 

 few oil-globules and nothing of this molecular basis. Just as in fact lymph 

 is, broadly speaking, blood minus its red corpuscles, so chyle is lymph plus 

 a very large quantity of minutely divided neutral fat. 



The total amount of lymph or of chyle which enters the blood system 

 through the thoracic duct, though it probably varies considerably, is prob- 

 ably also always very large. It has been calculated that in a well-fed animal 

 a quantity equal at least to that of the whole blood may pass through the 

 thoracic duct in twenty-four hours, and of this it is supposed that about half 

 comes through the lacteals from the alimentary canal, and therefore to a 

 large extent from food, and the remainder from the body at large. These 

 calculations are based on uncertain data, and cannot, therefore, be taken as 

 of exact value, but we may use them for the sake of an illustration. Thus, 

 in a man of average weight, that is, about 154 kilos., the quantity of blood 

 ( 38) being -^ of the body weight is about 12 kilos. The quantity of lymph 

 or chyle, therefore, discharged into the blood in an hour would be according 

 to this calculation half a kilo., or something less than half a litre; and since 

 the flow must vary considerably in the twenty-four hours would be sometimes 

 less, and therefore sometimes even more, than this. 



The Movements of Lymph. 



253. Making every allowance for the uncertainty of the calculations 

 detailed in the preceding paragraph, it is obvious that the lymph must flow 



