ABSORPTION FROM SEROUS CAVITIES 353 



conceivable that the glands change the substances in the liquid flowing through 

 them in some way. From the fact that they swell up under various patholog- 

 ical conditions we may also conclude that they retain injurious substances to 

 some extent and thus prevent their entrance into the blood stream. 



If the afferent and efferent vessels of a lymph gland be tied, but the blood 

 vessels be left open, the leucocytes in the gland disappear (Koeppe). From 

 this it would seem to follow that the lymph constitutes a stimulus for the lymph 

 gland, to which the latter responds by the formation of leucocytes (Asher and 

 Barbera). 



5. ABSORPTION FROM SEROUS CAVITIES 



Dissolved substances as well as water can pass from the lymph into the 

 blood vessels. This we know because solutions injected subcutaneously or in- 

 jected without injury into the blood vessels of a limb which is connected with 

 the rest of the body only by means of the blood vessels, are completely absorbed 

 (Magendie). 



Substances can also be absorbed from the serous cavities of the body, such 

 as the peritoneal space, the pericardial cavity, pleural cavity, etc. A fluid, 

 whether serous in character or not, and whatever its origin, when injected into 

 such a cavity is always first rendered isotonic with the blood plasma. If it be 

 hypertonic as e. g. a two-per-cent solution of NaCl to begin with, it is diluted 

 by the addition of water until it has exactly the osmotic pressure of the blood 

 plasma ; if it be hypotonic e. g., a 0.5-per-cent solution of NaCl it loses water 

 until it has the osmotic tension of a 0.92-per-cent KaCl solution, and then in 

 either case remains at this concentration until absorption is complete. 



These alterations of the osmotic pressure are unquestionably to be referred 

 to osmotic processes going on between the injected fluid and the blood plasma. 



It might be very naturally supposed that absorption from these cavities takes 

 place through the lymph spaces which open into them, and in the case of the 

 pleural cavities and the peritoneal space this seems to be quite readily demon- 

 strable. But absorption from the abdomen and the thorax can take place also 

 through the blood vessels, and in fact the latter seem to play the chief role here. 



Now, since the blood vessels can, as may be assumed without definite proof, 

 absorb fluids isotonic with their contents, one would be inclined at once to ascribe 

 the action to some specific vital activity of the endothelial cells. But the sur- 

 prising thing is that absorption from these cavities can take place to about the 

 same degree in dead animals as in live ones. Active cells therefore are not 

 essential to the process. 



There remains to be mentioned, besides the processes of diffusion and the 

 attractive power of proteid for water (cf. page 154), the process of imbibition. 

 All tissues, living as well as dead, have the power of taking up fluids either by 

 molecular imbibition i. e., of absorbing fluids through homogeneous substance 

 or by capillary imbibition i. e., through discrete pores. Hamburger supposes 

 that by imbibition of the first kind fluids are absorbed by the homogeneous 

 cement substance between the endothelial cells lining the peritoneum, and that 

 by the same process the fluid is passed on into the subepithelial connective tissue. 

 Also, that the cement substance between the endothelial cells of the capillaries 

 acts in the same way, and by means of the minute lumina of the capillaries an 

 imbibition by capillarity assists in draining the abdominal cavity. 



This power of imbibition, however, is limited and would soon come to a stop, 

 since a given volume of tissue could only take up a certain quantity of fluid. 



