i;o INTRODUCTION TO GENERAL PHYSIOLOGY 



Place a drop of each on a slide, and add a drop of blood, mixing 

 with a needle. The corpuscles in 10 per cent, solution (=0.3 

 molar) will be practically unaltered in size. Those in 5 per cent, 

 will be increased, those in 15 per cent, will be decreased. Since 

 the osmotic pressure of the serum is not always exactly the same 

 in different cases, some increase or decrease may be produced by 

 10 per cent, cane-sugar. If the former, try a slightly stronger 

 solution ; if the latter, a slightly weaker solution. 



Take 2 or 3 c.c. of 10 per cent, cane-sugar solution in a test- 

 tube. Add a drop of blood. The corpuscles will deposit gradually, 

 leaving the solution colourless. Add water slowly, noting how 

 much is added. At a certain dilution, the solution will begin to 

 become coloured with hemoglobin, owing to breaking up of the 

 corpuscles (Jicemolysis}. Note that the dilution required is greater 

 than corresponds to the solution in which the corpuscles maintain 

 their normal size (isotonic solution}. This is due to the fact that 

 they are able to swell to a notable degree before bursting. 



Similar experiments may be made with 0.3, 0.9, and 2 per cent, 

 sodium chloride. The isotonic solution will be found to be 0.9 per 

 cent. Note that a 0.3 molar solution is 1.75 per cent, and that 

 0.9 per cent, is only 0.154 molar. A 1.75 per cent, solution makes 

 the corpuscles shrink ; it is hypertonic. 



Next take a 0.3 molar solution of urea (=1.8 per cent.). It 

 causes haemolysis as if water. Dissolve the urea in 0.9 per cent, 

 sodium chloride ; no haemolysis occurs. Hence the effect of the 

 pure urea solution is not due to a toxic action of the urea, but to 

 the permeability of the corpuscles for urea. 



Saponin or ether, even in 0.9 per cent, sodium chloride, causes 

 haemolysis, which is due in these cases to a destruction of the 

 osmotic properties of the cell membrane. 



Take defibrinated blood, to be obtained from the slaughter- 

 house. Or better, cut off the head of a rat, collect the blood, and 

 stir it with a feather. Put about 10 c.c. into a graduated centrifuge 

 tube, and centrifuge until the volume of corpuscles, read off on the 

 scale, no longer changes its value. Pour off the serum, which is 

 probably slightly coloured with haemoglobin, so as not to disturb 

 the deposit. This may be done by using a glass rod touching the 

 lip of the tube. It does not matter if a little serum remains. Add 

 15 per cent, cane-sugar, shake up the corpuscles with it gently 

 and centrifuge again. The volume is less. Repeat with 5 per 

 cent, solution, the volume is increased as compared with the 

 original one. 



For this experiment a simple hand centrifuge, as sold by the 

 dealers, suffices. The haematocrite, in which smaller tubes are used 

 and spun at a greater rate, is used for small quantities of blood, 



