444 LESLIE B. AREY 



lished facts. Freezing point determinations have shown that 

 human blood plasma is isotonic with a sodium chloride solu- 

 tion of 0.85 per cent to 0.9 per cent in strength (Hamburger, '02; 

 Hober, '02; Dekhuyzen, '01), and, according to Hamburger, a 

 0.99 per cent solution is isotonic with rabbit's blood. If, therefore, 

 cups exist normally in the blood, why should discs be found exclu- 

 sively in isotonic saline solutions, whereas cups are first obtained 

 in hypotonic solutions of about 0.6 per cent? Weidenreich 

 explains away this discrepancy by assuming that there is an 

 elastic corpuscular membrane which varies in elasticity in salt 

 solution and in plasma.^ There was postulated a decreased 

 elasticity, due to a swelling of the membrane in salt solution, 

 which opposes the entrance of liquid, thereby preventing the 

 imbibition of as much water as should enter to bring the con- 

 tents of the corpuscle and the surrounding medium into equilib- 

 rium. In other words, the internal pressure of a corpuscle in 

 a 0.6 per cent sodium chloride solution is greater than the pres- 

 sure of the plasma by an amount corresponding to a 0.3 per 

 cent saline solution, and this is a measure of the tension exerted 

 by the decreased elasticity of the' corpuscular membrane. 



Additional evidence was presented in this 1903 paper. Among 

 other things it was stated that if blood, as it issues from a cut, 

 is drawn directly between two cover slips, and the preparation 

 rung with oil to prevent evaporation, isolated corpuscles appear 

 as typical cups. 



In 1905 a Weidenreich recommended another method for 

 demonstrating cups. Blood, obtained from an animal by de- 

 capitation or by blood letting, was defibrinated and centrifuged, 

 and in this serum blood was examined. Cups, not .discs, were • 

 observed. 



Heidenhain ('04) referring to Quincke, held that the effect of 

 colloids on the '' Molecular kraft" of a medium is important. 

 Starting from this clue Weidenreich ('05 a) reasoned that if the 



^ Weidenreich was influenced by the work of Koeppe ('99) who had shown by 

 hematocrit methods that the swelling of corpuscles in dilute salt solutions was 

 not as great as it should be if osmosis alone were responsible — due, he said, to the 

 elasticity of the membrane. 



