THEORIES OF L UD WIG AND HEIDENHAIN. 293 



somewhat increased. Hence the only region of the body below the 

 point of obstruction where the capillary pressure is not much diminished 

 is the liver. Now we find that the liver is also the sole source of the 

 lymph obtained under these circumstances. If the hepatic lymphatics 

 be ligatured, and the thoracic aorta be then obstructed, the now of 

 lymph from the thoracic duct is absolutely stopped. 



These three experiments show, therefore, that the lymph production 

 in the organs of the abdomen is directly proportional to the capillary 

 pressure in these organs, and not independent of them, as was imagined 

 by Heidenhain. 



Hydrcemia and hydrcemic plethora. In another series of experi- 

 ments we find, as was predicted by Ludwig (cf. p. 288), that a marked 

 increase in the lymph flow is produced by a general rise of capillary pres- 

 sure in all the organs of the abdomen. Such a general rise of capillary 

 pressure may be brought about by the injection of large quantities 

 of normal saline fluid into the circulation, thus causing a condition of 

 hydrcemic plethora. Under such circumstances the lymph may be in- 

 creased from fifty to one hundred times in amount, and may in some 

 cases run from the cannula in the duct in a steady stream. Now, in 

 hydraemic plethora there are two changes in the circulation which might 

 possibly be responsible for the increased production of lymph first, 

 the change in the composition of the blood, and secondly, the increased 

 pressure in the capillaries of the abdominal viscera. We can decide 

 which of these two factors is responsible for the increased lymph flow 

 by a very simple experiment. Previously to injecting 300 c.c. of normal 

 saline, we bleed the dog to 300 c.c., so that after the injection the total 

 amount of circulating fluid is the same as at the beginning of the 

 experiment. In this way we entirely avoid any rise of capillary 

 pressure, while we have diluted the blood to an even greater extent 

 than in the experiments in which hydrsemic plethora was produced. 

 The effect of such a simple hydrsemia is to increase the lymph flow 

 from 3 c.c. in ten minutes to 4 or 6 c.c. in ten minutes ; whereas, if 

 hydraemic plethora were produced, the lymph would be increased from 

 3 c.c. to 30, 50, or 100 c.c. in ten minutes. It is evident, therefore, that 

 in the production of this increased lymph flow the all-important factor is 

 the rise of capillary pressure ; although the slight increase in the lymph 

 flow observed as the result of simple hydrsemia shows that, as might be 

 expected, a watery plasma gives rise to a transudation of lymph more 

 easily than does the normal more concentrated plasma. 



Heidenhain s second class of lymphagogues. In a precisely similar 

 manner we may explain the mode of action of the substances which 

 were described by Heidenhain as the second class of lymphagogues. 

 These include bodies such as salt, sugar, potassium iodide, etc. The 

 injection of a strong solution of dextrose (30 grms. in 30 c.c. water) into 

 the veins of an animal causes a considerable increase in the lymph flow 

 from the thoracic duct. The lymph at the same time becomes more 

 watery than at the commencement of the experiment. Heidenhain 

 ascribes this effect to a specific excitation of the secretory activities of 

 the endothelial cells. The effect, however, can be explained in a much 

 more simple fashion. All these solutions have an osmotic pressure 

 which is considerably higher than that of normal blood plasma. A 

 solution of dextrose that should be isotonic with the blood plasma would 

 contain from 5 to 6 per cent, of this body. When we inject a solution 



