74 AN AMERICAN TEXT-BOOK OE PHYSIOLOGY. 



blood-plasma also becomes more watery, thus indicating that the increase in 

 water comes from the tissues themselves. Heidenhain designated these bodies 

 as " Ivmphagogues of the second class." His explanation of their action is 

 that the crystalloid materials introduced into the blood are eliminated by the 

 secretory activity of the endothelial cells, and that they then attract water 

 from the tissue-elements, thus augmenting the flow of lymph. These sub- 

 stances cause but little change in arterial blood-pressure, hence Heidenhain 

 thought that the greater flow of lymph could not be explained by an increased 

 filtration. Starling 1 has shown, however, that, although these bodies may not 

 seriously alter general arterial pressure, they may greatly augment intracapil- 

 lary pressure, particularly in the abdominal organs. His explanation of the 

 greater flow of lymph in these cases is as follows : " On their injection into 

 the blood the osmotic pressure of the circulating fluid is largely increased. In 

 consequence of this increase water is attracted from lymph and tissues into the 

 blood by a process of osmosis, until the osmotic pressure of the circulating 

 fluid is restored to normal. A condition of hydremic plethora is thereby pro- 

 duced, attended with a rise of pressure in the capillaries generally, especially 

 in those of the abdominal viscera. This rise of pressure will be proportional 

 to the increase in the volume of the blood, and therefore to the osmotic pres- 

 sure of the solutions injected. The rise of capillary pressure causes great 

 increase in the transudation of fluid from the capillaries, and therefore in the 

 lymph-flow from the thoracic duct." This explanation is well supported by 

 experiments, and seems to obviate the necessity of assuming a secretory action 

 on the part of the capillary walls. 



5. One of the most interesting facts developed by the experiments of Hei- 

 denhain and his pupils is that after the injection of sugar or neutral salts in 

 the blood the percentage of these substances in the lymph of the thoracic duct 

 may be greater than in the blood itself. It is obviously difficult to explain 

 how this can occur by filtration or diffusion, since it seems to involve the pas- 

 sage of crystalloid bodies from a less concentrated to a more concentrated solu- 

 tion. Cohnstein 2 has endeavored to show a fallacy in these results. He con- 

 tends that since it requires some time (several minutes) for the lymph to form 

 and pass into the thoracic duct, it is not justifiable to compare the quantitative 

 composition of specimens of blood and lymph taken at the same time. If one 

 compares, in any given experiment, the maximal percentage in the blood of 

 the substance injected with its maximal percentage in the lymph, the latter 

 will be found to be lower. This, however, does not seem to be the case in all 

 the experiments reported. The work of Mendel s with sodium iodide seems to 

 establish the fact that when this salt is injected slowly its maximal percentage 

 in the lymph may exceed that in the blood; and in the experiments made by 

 Cohnstein, as well as those by Mendel, it is shown that the percentage of the 

 substance in the lymph remains above that in the blood throughout most of 

 the experiment. In this point, therefore, there seems to be a real difficulty in 



1 Op. fit. 2 Archiv fur die cjemmmtc Physiologie, 1894-95, Bole, lix., lx. and lxii. 



s Journal nf Phi/xiology, 1896, vol. xix. p. 227. 



