Chap, i.] TISSUES AND MECHANISMS OF DIGESTION. 403 



though whether the small quantity of soaps and of lecithin 

 present is greater than in lymph has not been distinctly ascer- 

 tained. Cholesterin is probably present in greater amount than 

 in lymph, since it probably comes from the bile poured into the 

 intestine during digestion ; but this is not certain. How far 

 the nature of the fat, that is, the proportion of the various kinds 

 of fat, of stearin, &c, 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 vari- 

 ous sizes, but all small. A very considerable quantity however 

 is present in the form of exceedingly minute spherules or gran- 

 ules, 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 intes- 

 tine, 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 shews besides the white corpus- 

 cles 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 con- 

 siderably, is probably also always very large. It has been cal- 

 culated that in a well-fed animal a quantity equal at least to 

 that of the whole blood may pass through the thoracic duct in 

 24 hours, and of this it is supposed that about half comes 

 through the lacteals from the abdominal viscera, 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 aver- 

 age weight, that is, about 70 kilos, the quantity of blood (§ 38) 

 being Jg- of the body weight is about 6 kilos. The quantity of 

 lymph or chyle therefore discharged into the blood in an hour 

 would be according to this calculation a quarter of a kilo, or 

 something less than a quarter of a litre ; and since the flow 

 must vary considerably in the 24 hours, would be therefore 

 sometimes less and sometimes even more than this. 



The Movements of Lymph. 



§ 242. Making every allowance for the uncertainty of the 

 calculation detailed in the preceding paragraph, it is obvious that 



