80 TOXIN AND TOXOID 



dose of a toxin to be 0*003, an d the L dose 0-305 (= 100 lethal 

 doses). Nine months later the L dose was still 0305, whilst 

 the minimal lethal dose was 0-009 c - c - (=33*3 lethal doses only). 

 Thus, the toxin had fallen to one-third of its former toxicity, but 

 had retained its power of combining with antitoxin unaltered ; and 

 it is found that the two numbers usually bear some simple ratio 

 to one another e.g., i - ^ or i J, as in the previous examples. 



We are now in a position to understand all Ehrlich's results, 

 and especially the proof that a molecule of toxin consists of two 

 parts a haptophore group, which has the power of combining 

 with antitoxin or with the protoplasm of the body cells, but which 

 has in itself no lethal action ; and a toxophore group, which has 

 the power, when linked to a body cell by means of the haptophore 

 group, of causing toxic symptoms, probably by a process akin to 

 enzyme action. This toxophore group is unstable, and when it is 

 decomposed the toxin molecule is converted into toxoid ; it then 

 retains its power of uniting with antitoxin and with the tissue 

 cells, but is devoid of toxicity. Further, there are many varieties 

 of toxin, which differ from one another (i) in their avidity for 

 antitoxin, and presumably for the tissue cells ; (2) in the readiness 

 with which they are decomposed into inert toxoid; and (3) in 

 their toxic action, in that true toxins cause rapid death, local 

 inflammation, necrosis, etc., but no paralysis, whilst toxons 

 produce only transient soft oedema and subsequent paralysis. 

 Lastly, Ehrlich supposes that toxin and antitoxin have a great 

 affinity for one another, so that their combination resembles that 

 of a strong acid with a strong base, and the compound toxin- 

 antitoxin molecule when once formed does not dissociate, but 

 remains as a stable substance. It is on this point that his views 

 differ from the more recent ones of Arrhenius and Madsen, who 

 regard the union as being akin to that of a weak acid and a weak 

 base. We hope to be pardoned if, before describing their experi- 

 ments and conclusions, we give a brief outline of the difference 

 between the two reactions. 



According to modern chemical theories, most substances in 

 watery solution decompose into ions, atoms or groups of atoms 

 carrying an electrical charge. Thus, a solution of hydrochloric 

 acid contains ions of H carrying a positive charge and of Cl 

 carrying a negative one. Different substances undergo ionization 

 to a different degree. Thus, HC1 and NaOH are ionized to a 

 great extent, boracic acid and ammonia hydroxide but slightly. 



