EED BLOOD CORPUSCLES 7J 



becomes crenated. The rapidity and extent of the collapse and 

 consequent crenation appear to be dependent upon the degree of 

 hyperisotonicity produced, and the consequent volume of the out- 

 ward osmotic flow. 



Normal Saline Solution (isotonic). It is possible to produce a 

 saline solution whose specific gravity corresponds with that of the 

 plasma, and which is isotonic for the corpuscles. An aqueous 

 solution of this character contains about 0.9 per cent of sodium 

 chlorid. The exact strength of such a solution can not be accu- 

 rately stated, for the reason that the tonicity of the blood plasma 

 not only varies somewhat in different individuals, but also in the 

 same individual at different times and under varying conditions 

 of diet, absorption, excretion, etc. 



An isotonic solution, when added to the blood, will be found 

 to produce no visible change in the appearance of the blood cells. 



Certain reagents, as well as extremes of heat and cold, have 

 the property of rapidly dissolving out the hemoglobin, laking the 

 blood, either by rupture or by solution of the corpuscular envelope. 

 Such reagents are dilute acids or alkalis, bile, and the serum from 

 a different species of animal ; the last-mentioned reagent possesses 

 a certain forensic value in determining the animal species of a 

 given specimen of blood. These reagents, when mixed with 

 human blood, produce a rapid destruction of its corpuscles 

 hemolysis. 



These osmotic peculiarities, taken in connection with other 

 facts e. g., the presence of a cell membrane in the red blood cells 

 of animals beneath the mammalian type ; the extreme elasticity of 

 the corpuscle, which can be distorted into almost any conceivable 

 shape, but returns immediately to its original form ; and the tend- 

 ency of the corpuscles in undiluted blood to adhere to each other 

 in the form of moniliform piles, rouleaux, like rolls of coin, their 

 cohesion being apparently due to the presence in their envelope 

 of cholesterin and lecithin, which possess the physical properties 

 of a fat would seem to demonstrate beyond a doubt the presence 

 in the red blood cell of an outer exoplasmic envelope differing in 

 structure and in composition from its contained endoplasm. 



Development of the Red Blood Cell. The earliest embryonic 

 origin of the red blood corpuscle is a much disputed point. Ac- 

 cording to van der Stricht,* however, they first appear in the 



* Compt. rend. soc. de biol., 1895. 



