254 PHYSIOLOGICAL CHEMISTRY. 



serve to detect an abnormality in the blood more readily than 

 this may be accomplished by chemical analysis. It is custo- 

 mary at the present time to designate this freezing point de- 

 pression by A. Thus, normally, for human blood 



A = 0.56. 



ISOTONIC COEFFICIENT. 



When a few drops of blood are mixed with an excess of 

 salt solution of a certain strength and the mixture allowed to 

 stand at rest the corpuscles gradually settle and leave a color- 

 less liquid above. If the same volume of a certain weaker 

 salt solution is taken with the blood the mixture after shaking 

 is found to leave no longer a colorless liquid above the settled 

 corpuscles, but a somewhat reddish liquid. This color shows 

 that the corpuscles have been broken and that a little of the 

 hemoglobin has escaped. An experiment will illustrate the 

 fact; it is due to Hamburger. 



Ex. Prepare a series of common salt solutions of the following 

 strengths : 0.7 per cent, 0.65 per cent, 0.60 per cent, 0.55 per cent, 0.50 per 

 cent and 0.45 per cent. Measure out accurately 20 cc. of each into test- 

 tubes and add to each 5 drops of defibrinated bullock's blood. Shake and 

 allow to stand. Notice that in some of the tubes the corpuscles have 

 settled, leaving the salt solution practically clear and colorless ; in others 

 there is color, which is greatest in the tube with the least salt. In the 

 tube with 0.60 per cent of salt there should be no color, while in the tube 

 with the next weaker solution some appears. There must be therefore 

 some solution between these two in which the corpuscles just fail to give 

 up color. Hamburger found this to be one with 0.58 per cent of salt. 



Osmotic Tension. Hamburger made a large number of 

 experiments of this description and found the limiting value 

 of the strength of solutions for which no loss of color follows. 

 He spoke of these solutions as being isotonic, or as having the 

 same osmotic tension as the contents of the corpuscles. The 

 numerical values found bear a close relation to the molecular 

 weights of the salts used. Thus, the following values were 

 noted : 



