ANIMAL CHEMISTRY. 



411 



Fig. 119. 



to stand. But if we add salt to the water in the tube, the solution thus made 

 will in a few minutes rise in the tube, while the water in the vessel will 

 fall. This is because some of the water, attracted by the 

 solution of salt, passes through the pores of the bladder. 

 The salt has given the water in the tube something like a 

 power of suction. We can vary this experiment in several 

 ways. If the salt be put into the vessel, the contrary effect 

 will be produced the water in the tube will fall below the 

 level of the fluid in the vessel. If salt be put into both ves- 

 sel and tube in equal proportions, no change will follow ; 

 but if in unequal proportions, the suction will be toward the 

 strongest solution. Suppose now that instead of salt you 

 put a solution of gum or sugar into the tube, holding it so 

 that the level shall be the same with that of the water in 

 the vessel. Here the fluid in the tube will rise, because the 

 water from without presses in through the bladder. This 

 passing inward is called by Dutrochet, who first developed 

 this subject, endosmose, from two Greek words endon, inward, and osmos, 

 impulsion, or pressure. But some of the gum or sugar is found, after a 

 time, in the water outside. There is, therefore, also a transmission from 

 within outward, though less than that from without inward, and this he 

 called exosmose, ex meaning from or outward. The membrane used in 

 such experiments is called the septum. Similar phenomena are seen with 

 other substances ; as, for example, albumen, a substance which is largely 

 present in animals. You can readily see, then, that the agency which we 

 have described must have a very wide influence on the circulation of fluids 

 in both the animal and vegetable world, for salt, gum, sugar, albumen, etc., 

 are common substances in these fluids, and there are soft and porous mem- 

 branes every where ready for this endosmotic and exosmotic action. And 

 we may remark, in passing, that the influence of this agency is very consid- 

 erable, also, in the mineral world, for gases as well as liquids are affected 

 by it, and it may act through almost any porous substance. 



583. Circulation of Matter. You have seen in this book 

 that in the ministration of nature to the wants of man and 

 other animals there is a constant circulation and inter- 

 change of matter between the three kingdoms of nature. 

 First there is a circulation in the strict sense of that word, 

 for there is a movement in a circle. As the vegetable re- 



