REACTIONS BETWEEN ANTIBODIES 25 



much more rapidly than the antitoxins, which are often said 

 not to diffuse. Madsen and I have made an investigation 

 of this phenomenon. In common test-tubes a 5 per cent 

 solution of gelatine was poured to a height of about 10 cm. 

 This solution solidified in a refrigerator. After this a solu- 

 tion of toxin or antitoxin was added to a height of 1.3 cm. 

 above the column of gel, and the test-tube placed on ice 

 (mean temperature 6 C.), where it remained for sometime, 

 (from one to four or more weeks) according to the diffu- 

 sibility of the substance. After this the fluid solution and 

 the different layers of the column of gel were analysed for 

 their content of the different substances. By the aid of 

 these determinations it is possible to calculate the diffusion 

 constant of the substances examined. In this way we 

 found the following constants, valid for 12 C. and expressed 

 in days and centimeters : 



Sodium chloride 0.94 



Diphtheria-toxin 0.014 



Diphtheria-antitoxin .... 0.0015 



Tetanolysin 0.037 



Antitetanolysin 0.0021 



To the theoretical meaning of these figures we shall 

 return later. 



The very slow diffusion of the other substances as com- 

 pared with that of sodium chloride is evidently connected 

 with their high molecular weight. This is probably of the 

 same order of magnitude as that found by E. W. Reid 1 



1 E. W. Reid : Journ, of Physiology, 33. 13 (1905). The molecular weight 

 was calculated from the osmotic pressure of a I per cent solution. This pres- 

 sure was found to be 3.85 mm. at 15 C 



