METHODS OF ELECTRICAL STIMULATION 23 



by shaking, taking care that the mixture does 

 not foam too much. 



In each of six other test-tubes place 8 c.c. 

 sodium chloride solution of 0.62, 0.61, 0.60, 0.59, 

 0.58, and 0.57 per cent, respectively. Into each 

 tube let fall three drops of the same defibrinated 

 blood. Mix as before. After some hours the 

 red corpuscles will have settled to the bottom 

 in all the tubes. 



In the first series the clear fluid will be red 

 in some of the tubes. For example, the fluid in 

 the tubes diluted with 3.1, 3.0, and 2.9 c.c. water 

 may be red, while in the three other tubes it may 

 not be red. In this case the mixture of 5 c.c. 

 serum + 2.9 c.c. water has caused the haemo- 

 globin to escape from the corpuscles ("laked" 

 the blood), while the mixture of 5 c.c. serum 

 -f 2.8 c.c. water has not accomplished this. 



If the tubes with salt solution be now exam- 

 ined, escaped haemoglobin will be found only in 

 the 0.58 per cent and the weaker 'solutions. Con- 



29 + 28 

 sequently the mixture of 5 c.c. serum + - ~ 



water is isotonic with a sodium chloride solution 



, 0.59 + 0.85 

 of - - 0.585 per cent. Hence the un- 



2 



diluted serum is isotonic with a sodium chloride 

 solution of 5 + c 2 ' 85 x 0.585 = 0.92 per cent. 



