32 A TEXTBOOK OF PHYSIOLOGY 



water swells greatly and becomes a jelly. Imbibition plays a great 

 part in the vital phenomena of cells. Each cell has a normal water 

 content, which, however, may vary within certain limits according 

 to the tissue. Withdrawal of water below the normal limits impairs 

 the cell processes, which are either suspended for the time being, as 

 in the case of the spores of bacteria, or altogether destroyed. With- 

 drawal of 15 per cent, of water rapidly from a frog, or of 33 per cent, 

 slowly, stops all its cell activities. If, however, the amount of water 

 in a cell rises above its normal upper limit, its activities are also im- 

 paired; it becomes water-laden and boggy, or, to use the scientific 

 term, " cedematous." The power of a cell to regulate its water con- 

 tent is largely due to the phenomenon of " imbibition." In this 

 phenomenon, perhaps the electrical charge, and repulsion of the 

 particles, of the colloids of the cells are chiefly concerned, and exert 

 the pull which draws the water into the cell. The process is different 

 from osmosis, since the addition of certain salts to the colloid, instead 

 of aiding the passage of water, tends to hinder it. Electrolytes, 

 which favour the aggregation of a colloid, oppose the imbibition of 

 water by it, and vice versa. The cells e.g., secreting cells of glands 

 are confined by more or less rigid membranes, and the force of imbibi- 

 tion may be used to do work such as secretion. When a tissue becomes 

 cedematous, the normal imbibition power of the tissues is altered; 

 for example, owing to an alteration of the reaction of the tissues in 

 an acid direction, the proteins of the cell exert increased imbibitory 

 power, and thus become " cedematous " or " water-logged." Thus, 

 the dead eye of an ox placed in faintly acid water becomes tensely 

 swollen. Such swelling is hindered by the addition of sodium citrate. 

 So, too, if the hind-leg of a frog be ligatured so that the blood-supply 

 is cut off, and the animal placed in water, the ligatured hind-limb 

 swells up to three or four times the normal size. If placed in a dry 

 vessel, the limb decreases in size, almost drying up If removed from 

 the body and placed in water, it swells up again to a great size. 



The muscles of a frog swell when exposed to a pressure of water 

 over 350 atmospheres, and lose their contractile power. This may 

 return if the excess of water is at once dried off. Exposure to such 

 pressures kills all terrestrial and shallow-water life, except that of 

 spore-bearing bacteria, by a kind of water coagulation. The bacteria 

 are protected by their tough membrane. The deep sea fishes which 

 live at depths of two miles or more must be immune to such water- 

 pressures. 



