328 ABSORPTION. 



in explanation of the important influence of the nervous system upon this function. Pre- 

 cisely how the nervous system affects absorption, in all instances, it is impossible, in the 

 present state of our knowledge, to determine ; but modifications are frequently effected 

 through the sympathetic nerves. These nerves, as is well known, are capable of pro- 

 ducing important local changes in the circulation, and can even temporarily arrest the 

 capillary circulation in some parts ; and it is in this way that many of the variations in 

 absorption may be produced. 



Lymph and Chyle. 



To complete the history of physiological absorption, it will be necessary to treat of 

 the origin, composition, and properties of the lymph and chyle. It is only within a few 

 years that physiologists have been able to appreciate the importance of the lymph, for 

 the experiments indicating the enormous quantity of this liquid which is continually 

 passing into the blood are of recent date. The earlier experimenters never succeeded in 

 obtaining more than a small quantity of fluid from the lymphatic system. On the other 

 hand, for the long period during which it was supposed that all the products of diges- 

 tion entered the system by the thoracic duct, the importance of the chyle was much 

 exaggerated ; but the researches upon intestinal absorption by Magendie and those who 

 followed him, and the experiments of Colin on the quantity of fluid which passes into 

 the blood by the thoracic duct during the intervals of digestion, have enabled physiologists 

 to form a better estimate of the importance of the lymph and chyle. In studying the 

 properties of these fluids, the consideration of the lymph naturally precedes that of the 

 chyle, as the latter consists simply of lymph, to which certain of the products of diges- 

 tion have been added by absorption from the alimentary canal. 



Mode of obtaining Lymph. The old methods of obtaining this fluid are no longer 

 employed. In the inferior animals, recently killed, a few drops may be obtained by 

 pricking the lymphatic glands or by exposing the right lymphatic trunk or the thoracic 

 duct and collecting the small quantity of fluid which is discharged when these vessels are 

 punctured. Although a notable quantity of chyle can be obtained from the thoracic duct 

 of an animal killed during intestinal absorption, it is difficult to collect even a small quan- 

 tity of fluid during the intervals of digestion. Various occasions have presented them- 

 selves for obtaining lymph, possessing more or less of its normal characters, from the 

 human subject during life ; but, in many of these instances, there existed some pathologi- 

 cal condition of the lymphatic system, and it cannot be assumed that the liquid thus 

 obtained was in a perfectly healthy condition. 



The first successful experiments in which the lymph and chyle were obtained in quan- 

 tity were made by Colin. This observer, in operating upon large animals, particularly 

 the ruminants, experienced no great difficulty in isolating the thoracic duct near its junc- 

 tion with the subclavian vein and introducing a metallic tube of sufficient size to allow 

 the free discharge of fluid. These experiments, made upon horses and the larger rumi- 

 nants, were the first to give any clear idea of the quantity of liquids (lymph and chyle) 

 which pass through the thoracic duct. In an observation upon a cow of medium size, he 

 succeeded in collecting, in the course of twelve hours, the enormous quantity of 105-3 Ihs. 

 av. (47,963 grammes) ; and he farther states that a very much greater amount can be 

 obtained by operating upon ruminants of larger size. Whether this represent the actual 

 quantity which is normally discharged into the venous circulation, is a question which 

 will be considered under the head of the probable quantity of lymph and chyle ; but it 

 certainly shows that the lymph cannot but be regarded as one of the most important of 

 the animal fluids. 



Among the observations upon the fluids discharged from the thoracic duct, which 

 followed the experiments of Colin, the most interesting are those made in 1859, by Dai- 

 ton, who operated upon carnivorous as well as herbivorous animals. These experiments 



