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LESLIE B. AREY 



those already described when human serum was used. This 

 result supports the standard freezing point determinations of 

 Hamburger ('02), Hober, ('02) and Dekhuyzen ('02) which find 

 human plasma isotonic with an 0.85 to 0.9 per cent saline solu- 

 tion. On the contrary it militates directly against the conclu- 

 sion of Weidenreich and Lewis, who, notwithstanding the deter- 

 minations just alluded to, hold that a 0.6 to 0.65 per ctnt^f-alt 

 solution is isotonic with human plasma; these workers have 



Fig. 1 Profile sketches illustrating the shape assumed by the human erythro- 

 plastid in various dilutions of human serum with water. A, in undiluted serum > 

 B, ca. 25 per cent water; C, ca. 40 per cent water; D, ca. 50 per cent water; E, 

 ca. 60 per cent water; F, ca. 65 per cent water; G, ca., 70 per cent water. 



arrived at this point of view in the following way: blood issuing 

 from the veins is supposed to change suddenly from the cup 

 to the disc shape, due presumably to a slight concentration 

 through evaporation (or to loss of heat; Lewis?); on introducing 

 drawn blood or blood diluted in 0.9 per cent salt solution saline 

 discs become cups, hence the cup shape is normal and a 0.6 per 

 cent salt solution is isotonic with plasma. 



It was found that erythroplastids not only assume shapes 

 which are correlated with the concentration of the medium but 

 that these changes are also repeatedly reversible. Typical 

 experiments will illustrate this behavior. 



