70 FILTRATION EXPERIMENTS 



that the agglutinative action of ricin on red blood-corpuscles 

 could be inhibited in vitro by means of the serum of an immunized 

 animal. Kanthack showed that the action of snake -venom in 

 inhibiting the coagulation of blood was similarly prevented in 

 vitro by its appropriate serum, whilst Kossel and others did the 

 same for the haemoglobin of eel's blood, and Ehrlich for 

 tetanolysin. The previous cases were not of true bacterial toxins, 

 and might possibly be open to objection on that account. The 

 experiment of Neisser and Wechsberg on the effect of leucocidin 

 on leucocytes in vitro, and its inhibition by means of an antiserum, 

 is another case in point. It is true that in this case the leucocytes 

 are living, but we can hardly imagine that they have become 

 immunized by the action of the serum, or that the phenomenon 

 can be explained on any hypothesis other than that the toxin and 

 its antiserum have combined. 



The second and most important series of researches are those 

 of Martin and Cherry, who show that several toxins (e.g., that 

 of diphtheria and snake-venom) pass through a porcelain filter 

 which is impregnated with gelatin, whereas their appropriate 

 antitoxins, being composed of larger molecules, do not. (This had 

 previously been proved by Brodie.) They found, further, that 

 when a mixture of toxin and antitoxin was placed on such a filter 

 the first portion of the filtrate was toxic, but that the amount 

 diminished, and all toxicity disappeared a few minutes after the 

 mixture had been made. The inference is clear : the toxin had 

 united with the antitoxin to form a molecule as large as, or even 

 larger than, that of the latter, and therefore, like it, unable to pass 

 through the pores of the filter. These researches have been 

 confirmed by Brodie, and form, on the whole, the most striking 

 direct proof of the union of the two substances yet brought 

 forward. 



Calmette found that snake-venom is more heat-resistant than 

 its antitoxin, withstanding a temperature of 80 or 90 C., whereas 

 the latter is rendered inert at 68 C. He was then able to show 

 that a neutral mixture of the two could be rendered toxic again 

 by exposure to a temperature of 70 C. ; and this fact was used first 

 as an argument against the chemical theory of combination, and 

 secondly as a proof that the toxin is not destroyed when it unites 

 with antitoxin. As a matter of fact, neither inference is 

 necessarily correct, and the experiment was shown by the further 

 researches of Martin and Cherry to constitute a proof of the 



