216 OF ABSORPTION AND SANGUIFICATION. 



tained from the head and neck of the dog is estimated by Krause 1 at oue- 

 third, and by Weiss 2 at one-fifth of the weight of those parts; but these pro- 

 portions are probably too high for the body generally ; other experiments of 

 Weiss showing that it varies from one-fifth (after an abundant supply of 

 milk) to one-twelfth of the total weight. Bidder and Schmidt 3 estimated 

 that in man nearly thirty pounds of mingled lymph and chyle are daily 

 poured into the subclavian vein. 



155. The movement of the fluids taken up by the Absorbent vessels seems 

 to depend upon a combination of different agencies. The lower Vertebrata 

 are provided with "lymphatic hearts," 4 or pulsatile cavities, by which impor- 

 tant assistance is given to the onward flow; but no such aid is afforded in 

 Man or in the Mammalia ; yet it is obvious that a considerable vis a teryo 

 must exist, since, if the thoracic duct be tied, it is speedily distended below 

 the ligature, even to bursting. In the Lymphatics as well as in the Lac- 

 teals of the higher animals, the onward course of the contained fluids is 

 probably aided by the contraction of the uustriped muscular tissue in their 

 walls, assisted by the action of the valves; and to this perhaps we may at- 

 tribute the emptiness of the absorbent system which usually presents itself 

 some little time after death. Moreover, in all the movable parts of the 

 body, material assistance is afforded (as it is to the circulation in the veins) 

 by the occasional pressure exercised upon the lymphatic vessels by the sur- 

 rounding tissues (as the muscles, Paschutin); for while this pressure is op- 

 erating it will tend to empty them of their contents, which are only per- 

 mitted by the valves to pass in one direction; and when the pressure is 

 relaxed, they will be refilled from behind. In the lacteals, special agents for 

 the propulsion of the chyle exist in the muscular fibres contained within the 

 villi, which constitute so many minute force-pumps that are perhaps stimu- 

 lated to action (as suggested by Schiff) by the irritating properties of the 

 bile. When the lacteal and lymphatic fluids have arrived at the thoracic 

 duct, besides the forces already mentioned, their flow receives an additional 

 impetus from a vis a fronte derived in part from the suction-power exerted 

 by the rapid movement of the blood in the subclavian veins, the influence 

 of which may readily be proved experimentally, and partly from the nega- 

 tive pressure exerted upon the walls of the duct during the period of inspi- 

 ration, the opposing influence of expiration being neutralized by the valves. 5 

 Noll f> found the pressure in the larger lymphatics of the neck in cats and 

 dogs to be equal to that of a column of water varying from $ to 11 inch in 

 height (10 30 mm.), but it is probably much higher in the smaller vessels. 

 The rapidity of the current in the lymphatics of the neck is stated by Weiss 

 to be about one-sixth of an inch per second. 



156. Since the bloodvessels constitute a closed system of canals interposed 

 between the histological elements of .the various organs, a continual process 

 of transudation must take place through their walls, in order that the fluids 

 appropriate to the nutrition of the different tissues may be supplied in due 

 proportion to their requirements. This effect is probably in part the result 

 of the operation of the laws of Osmosis, which are here made subservient, 

 not only to the passage of the nutrient materials of the blood outwards, but 

 also to the introduction of the products of disintegration into the circulating 



1 Zeits f. rat. Med., Bd. vii. p. 148. 2 Virchovv's Arcbiv, B. xxii. 



8 Verdauungssafte und Stoffweolisd, ^ 224, 285. 



1 See \Vli:irton Jones on Lymphatic Heart of Eel, Proc. Roy. Soc., Nos. 98 and 

 101, 1868 



6 Dyl.Uwsky, Borieht. d. Sachs. Gcsdl., 1866. 

 6 L ucl wig, Physiologic, vol. ii, p. 581. 



