CIRCULATORY SYSTEM. 



117 



pile" rows. This is purely a physical phenomenon. As 

 soon as the oily covering dissolves this combination 

 disappears. The corpuscles are extremely susceptible 

 to changes in the plasma. If water is added they will 

 swell up and the hemoglobin begins to dissolve. With 

 evaporation the corpuscles begin to shrink, forming 

 minute processes and they are then said to be 

 crenated. Evaporation of water produces an in- 

 creased percentage of the salts 

 in solution. This in turn ab- 

 stracts water from the cor- 

 puscles and the shrinking or 

 crenated condition follows. 



It is estimated that the total 

 amount of blood in man is 



one-thirteenth the weight of the body. The average 

 normal male, therefore, has approximately 25,000,- 

 000,000,000 red corpuscles. The life period of a red 



i. Crenated red 

 orpuscles from man. 



Fig. 82. Red blood-corpuscle of frog; a, flat view; b, side view. 



corpuscle is not definitely known, but physiologists 

 tell us it is probably from two to four weeks. Ac- 



