THE CHEMICAL MECHANISMS OF DEFENCE 1155 



are just sufficient to neutralise 100 c.c. of acid, the addition of 50 c.c. 

 of alkali will leave half the acid unneutralised. If, however, we try 

 the same experiment in the case of mixtures of toxin and antitoxin, it 

 will be found that the addition of 50 c.c. of antitoxin will neutralise 

 much more than half of the toxin, and the same applies to other bodies 

 of this class. Ehrlich has attempted to explain this result by assuming 

 that in any toxin there is a mixture of substances, some having a 

 strong affinity for the antitoxin, and others, which he calls toxones, 

 possessing only a slight affinity. In the 50 c.c. of toxin first added 

 the toxins would satisfy all their combining powers, whereas the toxones 

 would not begin to combine until they were present in large excess. 

 Arrhenius and Madsen have drawn an analogy between the neutralisa- 

 tion of toxin by antitoxin and the neutralisation of a weak acid, such 

 as boracic acid, by a weak base, such as ammonia. They show that in 

 this case the general course of events would be similar to that observed 

 by Ehrlich. At no time would there be complete neutralisation, owing 

 to the fact that hydrolysis constantly occurs, so that when equivalent 

 quantities of each substance had been added, the fluid would still 

 contain a certain amount of free base alongside of free acid, in addition 

 to the salt produced by the combination of the two. It is impossible, 

 however, to account for all the phenomena presented in the neutralisa- 

 tion of toxin by antitoxin in this simple manner. Thus seventeen 

 parts of ammonia would neutralise exactly an equivalent quantity of 

 boracic acid, whether these substances were dissolved in 10 c.c. or 

 in 100 c.c. of water. If, however, it be found that 1 c.c. of antilysin 

 exactly neutralises 1 c.c. of lysin, these two substances will no longer 

 be in equilibrium when the whole is diluted up to 10 c.c. with water. 

 If a neutral mixture of lysin and antilysin be taken and filtered under 

 pressure through a gelatin filter, no lysin or antilysin passes through 

 the filter, so that the residue on the filter becomes concentrated. On 

 examining this residue it is found that it has a strong hsemolytic action, 

 and the same is true of the substance which may be obtained by 

 melting the gelatin out of the pores of the filter. It is evident that, 

 even in a neutralised mixture, both free lysin and free antilysin, or 

 free toxin and free antitoxin, are present, and it needs only the altera- 

 tion of the physical condition of the mixture in order to display the 

 action of one or other of these bodies. How then are we to regard this 

 combination of toxin with antitoxin ? Craw has pointed out that 

 the combination is in all respects comparable to that which occurs 

 between adsorbing surfaces and many dyestuffs. If we place some 

 filter paper in a solution of fuchsin or Congo red, the filter paper will 

 take up the dye substance. The amount taken up by the paper will 

 increase with increase in concentration of the solution. There will, 

 however, be a tendency to the formation of false equilibrium points, 



