IMBIBITION AND ENDOSMOSIS. 



323 



could never be detected. When the contents of the egg were replaced by the serum 

 of the blood, the same result followed. "After six or eight hours of immersion the 

 serum had yielded to the water in the vessel all its saline elements, chlorides, sulphates, 

 phosphates, which were easily recognized by their peculiar reactions, but 

 not an atom of albumen." 



A very simple apparatus for illustrating endosmotic action can be con- 

 structed in the following way : Remove carefully a circular portion, 

 about an inch in diameter, of the shell from one end of an egg, which 

 may be done without injuring the membranes, by cracking the shell into 

 small pieces, which are picked off with forceps. A delicate glass-tube, 

 about six inches in length, is then introduced through a small opening in 

 the shell and membranes of the other end of the egg, and is secured in a 

 vertical position by wax, the tube penetrating the yolk. The egg is then 

 placed in a wine-glass partly filled with water. In the course of half an 

 hour or an hour, the water will have penetrated the exposed membrane, 

 and the yolk w;ll rise in the tube. 



Influence of Membranes upon Osmotic Currents. The force with 

 which liquids pass through membranes, called endosmotic or osmotic 

 force, is to a great degree dependent upon the influence of the mem- 

 branes themselves. This influence is always purely physical, in experi- 

 ments made out of the body ; and physiological absorption can be ex- 

 plained, to a certain extent, by the same laws. It must be remem- 

 bered, however, that the properties of organic structures, which are 

 manifested only in living bodies, are capable of modifying these physical 

 phenomena to a remarkable degree. For example, all living tissues are 

 capable of selecting and appropriating from the nutritive fluids the ma- 

 terials necessary for their regeneration ; and the secreting structures of 

 glands also select from the blood certain principles which are used in 

 the formation of their secretions. At the present day, these phenomena and their modi- 

 fications through the nervous system cannot be fully explained. This is true, also, of 

 many of the phenomena of absorption and their modifications, which are probably de- 

 pendent upon the same kind of action. In view of these undoubted facts, the influence 

 of the structures through which liquids pass in physiological absorption may be divided 

 as follows : first, into physical influences, which may be illustrated by endosmotic ex- 

 periments with organic membranes out of the body ; and second, modifications of these 

 phenomena, which are presented only in the living organism. 



Numerous experiments have demonstrated that both the endosmotic and the exos- 

 motic current may be produced by using a porous instead of a membranous septum, 

 though then they are always comparatively feeble. The phenomena thus presented are 

 to be explained entirely by the laws of capillary attraction and of the diffusion of liquids. 

 These laws would enter largely into the explanation of the passage of liquids through 

 animal membranes, if it could be demonstrated, or even rendered probable, that these 

 membranes are invariably porous, or provided with capillary openings. It will be neces- 

 sary, however, to study this question very carefully and to examine all the properties of 

 animal membranes, both within and without the living organism. 



In the first place, is there any proof that all membranes which will admit the passage 

 of liquids are porous ? This is a most important question ; and it lies at the foundation 

 of the explanation of the phenomena of endosmosis by the laws of capillary attraction. 



In all membranes which possess an anatomical structure discoverable by the micro- 

 scope, there are undoubtedly interstices between the fibres, cells, etc., of which the tis- 

 sue is composed ; but, on the other hand, animal membranes generally have a layer, like 

 the basement-membranes of mucous tissues, which is absolutely homogeneous and struct- 



FIG. 97. Egg pre- 

 pared so as to il- 

 lustrate, wdos- 

 motie action. 



