I06 TETANUS TOXIN AND BRAIN-TISSUE 



in the case of tetanus, he supposed that antitoxin is formed by the 

 cells in the central nervous system, and explained the great difficulty 

 of immunizing animals to this toxin by pointing out the enormous 

 susceptibility of the cells to the action of this poison ; it is only 

 in the cells of the central nervous system that antitoxin can be 

 formed, and these cells are extremely easily killed by the toxin, 

 and are necessary for life. The chief evidence in favour of this 

 theory is derived from the experiments of Wassermann and of 

 Romer, which we shall now consider seriatim. 



Wassermann's experiment may be regarded as a corollary to 

 that of Ransom, who found that, after injection of tetanus toxin 

 in pigeons (which are, in the ordinary sense of the word, in- 

 susceptible to that substance), he could extract it from all 

 substances except the brain. Wassermann and Takaki found 

 that the mixture of tetanus toxin with an emulsion of the central 

 nervous system was no longer toxic when injected into susceptible 

 animals ; in other words, that the emulsion of central nervous 

 system behaved like antitoxin. Emulsions of other organs are 

 devoid of this power. They will combine with tetanus toxin, but 

 will yield it again when injected into susceptible animals or 

 macerated in salt solution. It appears, therefore, that the central 

 rjervous system is the seat, and the only seat, of an antitoxin-like 

 substance, and it is thus rendered at least probable that when 

 antitoxin appears in the blood it is due to its release from the 

 cells which contain it normally in other words, from the cells of 

 the central nervous system, the cells whichX attacks. The case 

 of tetanus is the only one in which a toxin appears to have a 

 definite selective influence on one group of cells, and is therefore 

 unique in providing a means whereby Ehrlich's supposition as 

 to the origin of antitoxin may be tested. It is no wonder that 

 Wassermann's experiment has been submitted to an extra- 

 ordinarily careful investigation, the results of which we must 

 outline briefly. Some of these experiments seem to point to the 

 truth of Ehrlich's assumption. Thus, Blumenthal showed that 

 after injection of tetanus toxin into living animals the spinal cord 

 lost its property of fixing the toxin in vitro, the receptors of the 

 cells being already occupied with that substance. Further, boiled 

 brain substance loses its power of neutralizing toxin, just as anti- 

 toxin does on being heated. He also showed that the central 

 nervous system of fowls, which are but slightly susceptible to 

 tetanus, has but little power of binding that toxin, so that emul- 



