REACTIONS BETWEEN ANTIBODIES 33 



tion process. If we picture to ourselves bacteria (or other 

 cells) of 5 to 10 /* diameter, shaken with the solution of 

 a substance which enters easily into the cells, we find that 

 even if the diffusion-constant of the substance be so small 

 as o.ooi, as for the least diffusible antitoxins, the process 

 of diffusion may reach its equilibrium in as short a time as 

 less than five minutes. 



We are led to similar results regarding the velocity of 

 reaction by some experiments of Madsen and Walbum. 

 They added cautiously a little quantity of a solution of 

 tetanolysin to 10 c.c. of a suspension of erythrocytes in a 

 test-tube, so that the solution remained in the uppermost 

 layers of the emulsion, and shook the test-tube after the 

 lapse of thirty seconds. In another experiment they added 

 the suspension precipitously to the poisonous solution, so 

 that the mixing took place immediately. The haemolysis 

 in the second experiment was nearly double that in the 

 first. This is explained by the fact that the tetanolysin 

 has a very much higher solubility in the erythrocytes than 

 in the surrounding medium. During the short time of thirty 

 seconds the uppermost erythrocytes had absorbed about 30 

 per cent of the poison, so that only about 70 per cent was 

 left for absorption by the larger fraction of the erythrocytes. 

 In consequence of the great absorption-coefficient of the 

 erythrocytes these retain nearly the quantity of poison 

 which they possessed at the moment of shaking, and the 

 final haemolysis was about as marked as if only 70 per cent 

 of the quantity of the poison used had been added in the 

 first experiment, supposing that it had been distributed 

 uniformly in the fluid. Other substances which are ab- 

 sorbed by erythrocytes or other cells seem to behave in 



