264 PHYSIOLOGICAL PHYSICS. [Chap. xxn. 



more rapidly than that of another existing already to 

 some extent in the circulating fluid. Thus variations 

 in the composition of the blood, variations which will 

 be determined by many circumstances, but very 

 specially by the matters that have been removed from 

 the blood to meet the demands of the tissues for 

 nourishment, will largely determine the rapidity of 

 the absorption. Among other things, if the blood 

 has been deprived of a considerable quantity of its 

 watery elements, its power of determining an osmotic 

 current towards itself will be largely increased. 



Special instances may now be given which illus- 

 trate these facts, and the great bearing of the 

 general laws of osmotic action. They are common 

 illustrations, but have been so clearly put by Baron 

 Liebig, in a work already referred to, that a few 

 paragraphs will be incorporated here. 



" If we take, while fasting, every ten minutes, a 

 glass of ordinary spring water, the saline contents of 

 which are much less than those of the blood, there 

 occurs, after the second glass (each glass containing 

 four ounces), an evacuation of coloured urine, the 

 weight of which is very nearly equal to that of the 

 first glass ; and after taking in this way twenty such 

 glasses of water, we have had nineteen evacuations of 

 urine, the last of which is colourless, and contains 

 hardly more saline matter than the spring water. 



" If we make the same experiment with a water 

 containing as much saline matter as the blood (three- 

 quarters to one per cent, of sea salt), there is no 

 unusual discharge of urine ; and it is difficult to drink 

 more than three glasses of such water. A sense of 

 repletion, pressure, and weight of the stomach point 

 out that water, as strongly charged with saline 

 matter as the blood, requires a longer time for its 

 absorption into the blood-vessels. 



" Finally, if we drink a solution containing rather 



