54 



LIFE: ITS BEGINNINGS AND NATURE 



membrane to swell and eventually burst 

 (Fig. 2-25). The water in which the cells 

 were placed is said to be hypotonic to the 

 blood cells. Hypotonic solutions should not 

 be injected into the blood stream of an ani- 

 mal because the destruction of red cells, as 

 well as others, could prove fatal. 



Again, if the cells were placed in a salt 

 solution in which the numbers of dispersed 

 particles were much greater than on the in- 

 side of the cell, the direction of flow would 



ever cells are placed in any kind of solution, 

 that the medium have the same number 

 of particles, or, in other words, it must have 

 the same osmotic pressure as the cells them- 

 selves, if severe trouble is to be averted. 



Another illustration of the effect of os- 

 motic pressure might be cited because of its 

 practical application. Perhaps you have 

 wondered why a person, floating upon vast 

 quantities of water, must die at sea if he 

 has no fresh water to drink. Sea water is 



physiologicol 

 salt soluVion 



distilled wotsr 



cor>c«ntro*Bd> 

 Solt solution > 



ISOTONIC 



HYPERTONIC 



HYPOTONIC 

 Fig. 2-25. The effect of salt solutions of various concentrations on the red blood cell. 



be in the opposite direction, namely, out of 

 the cell, causing it to shrink to only a frac- 

 tion of its normal size ( Fig. 2-25 ) . The rea- 

 son here is the same as in the previous case. 

 Such shrunken cells are called crenated 

 cells, and such a concentrated salt solution 

 is said to be hypertonic to the blood cells. 

 If such a hypertonic solution were injected 

 into the blood stream, it might also prove 

 fatal because of the wanton destruction of 

 blood cells. It is important, then, that when- 



heavfly laden with salts and its osmotic pres- 

 sure is considerably above that of the blood 

 and tissues of man and all other land ani- 

 mals. If, then, he should take sea water 

 into his stomach it would extract from his 

 stomach the precious water that is already 

 short, eventually filhng his stomach so that 

 he would be forced to throw it up. This 

 would leave his body with less water than 

 it had before he swallowed the sea water. 

 That is why drinking sea water can be fatal. 



