22 GENERAL PROPERTIES OF LIVING TISSUES 



per cent). From time to time remove the sec- 

 tions and observe under the microscope whether 

 plasmolysis is present. The serous fluid that 

 causes plasmolysis in half the cells immersed 

 in it, is isotonic or " normal " with the salt solu- 

 tion having the same effect. 



For example, if there were used 5 c.c. serum 

 + 1 c.c. water with 0.8 per cent solution of sodium 

 chloride, the original serum would be isotonic 



5-1-1 



with a sodium chloride solution of x 0.8 



5 



= 0.96 per cent. 



Should the osmotic pressure of the serum be 

 too slight to call forth plasmolysis in the cells 

 employed, add to the serum measured quantities 

 of a strong saline solution, e. g. 5 per cent sodium 

 chloride solution. 1 



2. The Hood-corpuscle method of Hamburger? 

 Place 5 c.c. serum in each of six test-tubes. 

 To these add from a burette 3.1, 3.0, 2.9, 2.8, 2.7, 

 and 2.6 c.c. water, respectively. Into each tube 

 let fall three drops of defibrinated blood, and mix 



1 HAMBURGER : Osmotischer Drnck und lonenlehre, 1902, 

 i, p. 438. 



The cells of Tradescantia cannot be used for the measure- 

 ment of osmotic pressure in acid solutions. For the urine, the 

 cells of Begonia manicata should be used. 



2 HAMBURGER : Loc. cit. pp. 185 and 439. Also Archiv fur 

 Physiologic, 1887, p. 31. 



