46 PHYSIOLOGY OF. THE DOMESTIC ANIMALS. 



its own volume of water may be absorbed. The gelatin must therefore 

 increase in volume. The fluid in organic imbibition passes into the inter- 

 molecular spaces and separates the molecules. That an organic body may 

 imbibe fluid it is consequently necessary that its molecules be freely 

 movable. 



The power of imbibition possessed by the organic tissues is espe- 

 cially due to their albuminoid constituents. Protoplasm is, therefore, 

 above all capable of imbibition, and the rapid formation or disappear- 

 ance of vacuoles in protoplasmic cells may be due to rapid changes in 

 imbibition. 



Every organic substance has a limit beyond which imbibition is 

 impossible. This limit is lower when the water contains solids in solu- 

 tion, provided the solids are not chemically acted on by the tissues, from 

 the fact that imbibed water is held with greater tenacity by the tissues 

 than are the substances held in solution in the water. Thus, when a 

 tissue saturated with a salt solution is subjected to pressure, the solution 

 first pressed out is more concentrated than that which is forced out when 

 the pressure is subsequently increased ; and in general the fluids lose in 

 concentration in imbibition. Organic tissues therefore absorb water with 

 greater readiness than saline solutions. The importance of this fact will 

 be seen in the explanation of osmosis. 



The extent of imbibition depends, therefore, on the membrane and 

 the nature of the fluid with which it is in- contact. Thus it has been 

 found by Liebig that one hundred parts of ox-bladder absorb, of — 



Water, . . . . 268 volumes. 



Salt solution (1.204 sp. gr.), . . .133 



Alcohol (84 per cent.), 38 



Marrow oil, . ... 17 " 



Membrane, therefore, has less affinity for a salt solution than for 

 water. This may also be shown by soaking a bladder in water, wiping 

 it dry, and then sprinkling it with common salt. The salt comes in 

 contact with some of the water in the bladder, dissolves, and forms a 

 salt solution. But as the membrane can contain less salt solution than 

 water, some of the solution is expelled and the bladder shrivels up. 

 So also a moistened bladder thrown into alcohol shrivels up, because 

 the alcohol mixes with the water in the bladder ; and as the bladder, 

 as shown above, can only absorb one-seventh as much alcohol as 

 water, the solution is driven out. This is the explanation of the use 

 of alcohol and various saline solutions for hardening tissues for making- 

 microscopic sections. 



In the nutrition of animal cells the process of imbibition is an 

 important factor. Every substance which is soluble in water is capable 

 of being appropriated by the protoplasm and may, through imbibition, 



