INTERREACTIONS OF TOXIN AND ANTITOXIN 75 



in which the oblique shading represents the toxic portions, as 

 before, and the horizontal shading represents the amount neutral- 

 ized by the addition of ^-^ c.c. of antitoxin ; the portion with 

 oblique but no horizontal shading represents the toxic portion 

 which remains unneutralized : it constitutes T J^ of the total 

 shaded portion, and is therefore i lethal dose. 



Such a finding may occur, but is unusual. In most cases we 

 find that the amount of toxin left free on partial neutralization is 

 subject to laws which are far more complex. In a case given by 

 Madsen and described in the same way we find : 



The addition of | parts of antitoxin left free no lethal substance 

 a term which we shall use for the present, instead of " toxin," 

 to denote the portion of the spectrum with the oblique shading. 

 In Ehrlich's language all had been neutralized except the toxon. 



The addition of $ left 5 units of lethal substance free ; it 

 follows that iS~ 2 9 ^j- = 2 fi oi7 had been necessary to neutralize 

 these 5 units. 



The addition of -f^ left 55 lethal units free ; hence, if after 

 the addition of -f^ (as above, leaving 5 lethal doses free) we add 

 an additional -/^, the difference (/<&) will neutralize 50 lethal 

 doses (55-5). 



Hence the additon of will just neutralize the remaining 

 lethal doses i.e., 45. 



To account for facts like these, Ehrlich suggests that the 

 solution contains four or five substances. The first i.e., that 

 which has the greatest power of combining with antitoxin, is called 

 prototoxin ; it is lethal, and it consists of two parts an a part, 

 which is readily changed into inert prototoxoid, and a ft part, 

 which is more stable, but which may, after a time, change into 

 prototoxoid also. These two modifications have exactly the same 

 affinity for antitoxin, so that if they were present in equal 

 amounts, and if all the a modification were changed into proto- 

 toxoid, each addition of antitoxin would go to neutralize active 

 prototoxin and inert prototoxoid in equal amount ; hence half of 

 it would apparently be wasted. 



Secondly, there is deuterotoxin, which also exists in an a and a /? 

 modification, of which the a part is readily transformed into 

 deuterotoxoid, whilst the (3 modification is very stable and is the 

 last lethal substance to disappear. The a and /3 modifications 

 have equal affinity for antitoxin, but this is less than that of the 

 prototoxin. 



