Physical Chkmistkv and Vktkuinary JScikxck. 179 



falls ; for instance, the average surface tension of fifteen horses at 

 37° C. suffering from horse-sickness was 5"85, whilst the normal value 

 (average from twenty-one horses) amounts to o-97. The suiface 

 tension of watin- at the same temperature is 7-132. 



The decrease of surface tension in grave cases of horse-sickness is 

 probably due to the accumulation of CO., in the blood, because it was 

 possible to repnxluce a simihir decrease Iw an artificial imitation of this 

 stage by strangulation of the jugular vein wherefrom the blood was 

 taken. 



Til. THE PHYSICAL-CHEMICAL LAWS OF SOLUTIONS. 



The chemical analysis of tlie licjuids of an organism demonstrates 

 the presence of a great number of crystalloids (sugar, urea, salts, as 

 cai'bonates, sulphates, chlorides, phosphates combined with potassium 

 sodium, calcium, magnesium). These crystalloids are all dissolved in 

 water ; we have to deal with watery nohitAonx. 



The peculiarities of solutions have been thoroughly studied during 

 the last thirty years, and tiie rules found in vitro by the physical- 

 chemical scientists have been proved to be the same, point by point, in 

 the living body. 



(«) Osmotic Pressure. 



Van 't Hofl' pointed out that a substance dissolved in water (or in 

 any other fluid medium) is in molecular dissemination, and acts as it 

 would do in a gaseous stage, namely, it has lost cohesion. The mole- 

 cules do not attract each otlier any more ; they are flying througli the 

 medium in all directions with great velocit}'^ like gas molecules do, and 

 exercise a pressuie against the wall which is called osmotic pressure 

 (corresponding to the gas tension). He showed that the three prin- 

 cipal physical laws of diluted gases are also applicable to diluted 

 solutions without regard to the chemical composition. They are as 

 follows : — 



(1) Boyle- Mar riotte — Van '< Hoff. — At a constant temperature the 

 pressure of a gas is proportional to its density ; or for solutions, the 

 osmotic pressure is proportional to the concentration. 



(2) Gay-Lu!^sac — Van V Hoff'. — The gas tension is proportional to 

 the absolute temperature, and increases at the amount of ^l^ for each 

 degree ; or, the osmotic pressure increases with each degree of rise in 

 temperature at the rate of 1 in 273. 



(3) Avoyadro — Van U Hoff'. — Ecjual volumes of difterent gases con- 

 tain at the same temperature and under the same pressure equal 

 numbers of molecules; or, solutions which at the same temperature 

 have the same osmotic pressure are equally concentrated. 



Plant physiologists with the so-called osometer have experimentally 

 demonstrated the truth of Van 't Hoif's theories. 



m2 



