THE ORIGIN OF ANTITOXIN THE SIDE-CHAIN THEORY 93 



antitoxin than it can neutralize. Thus Knorr showed that a 

 single unit of toxin might call forth 100,000 units of antitoxin. 

 This can scarcely be accounted for by supposing the transforma- 

 tion of the one substance into the other. 



2. It frequently happens that antitoxin occurs, sometimes in 

 considerable amounts, in the blood of animals that have not 

 received injections of toxin, and have not suffered, as far as 

 known, from the disease in question in other words, of " normal " 

 animals. Thus horses frequently have traces of diphtheria anti- 

 toxin in the blood, as much as 4 units per c.c. having been 

 observed. Metchnikoff suggests that this may be due to the 

 action of " pseudo-diphtheria " bacilli, which are so common. 

 But no one has been able as yet to produce diphtheria toxin or 

 symptoms of diphtheria by means of these bacilli, and it is not 

 usual to regard them as having any connection, other than a 

 superficial morphological resemblance, with the true diphtheria 

 bacillus. 



If we may bring other antibodies into the argument the case 

 against Metchnikoff's supposition is enormously strengthened. 

 The blood of many animals contains agglutinins and hsemolysins 

 often in large amounts, often under conditions in which we may 

 almost exclude the possibility of a preceding infection. Thus the 

 blood of a normal horse will almost invariably clump typhoid 

 bacilli, B. pyocyaneus, the cholera vibrio, and many other 

 organisms. 



3. An animal which has received an injection of antitoxin 

 rapidly eliminates it from the blood, whereas the antitoxin which 

 is formed in the body remains a much longer time. This argu- 

 ment does not carry very much weight, since, as Metchnikoff 

 points out, the toxin might remain for long periods occluded 

 in the cells, and only undergo a gradual transformation into 

 antitoxin. 



4. Roux and Vaillard showed that the whole of an animal's 

 blood might be removed by repeated venesections, and that the 

 newly regenerated blood might contain almost as much antitoxin 

 as was present before the haemorrhage, thus suggesting a new 

 formation. But the objection urged under the last heading is of 

 weight here also, and if we consider it probable that toxin may 

 remain latent in the tissues for long periods without causing 

 symptoms, we shall exclude this piece of evidence from the 

 argument, as well as the observations of Salomonsen and Madsen, 



