18 TOXINES AND ANTITOXINES. 



but only a relative one. The attractive power of the body cells 

 (receptors) shows a gradual decrease from the most susceptible 

 to the least susceptible animal. Thus tetanus poison, in a dose 

 many hundred times greater than is sufficient to kill a mouse, 

 circulates unchanged through the blood of a pigeon. If, how- 

 ever, still larger doses are given, the pigeon becomes ill. In this 

 case then there is not complete immunity, but only a very slight 

 power of attraction on the part of the receptors. According to 

 METSCHNIKOFF, 1 and FERMI and PERNOSSI (loc. cit.), certain cold- 

 blooded animals have still smaller powers of attraction. 



METSCHNIKOFF found that in the case of fishes, tortoises, and 

 alligators, and also of arthropoda, the toxine remained unaltered 

 in the blood without producing antitoxine. Only in the case of 

 alligators, after longer action (fifty-eight days), did he obtain any 

 antitoxine, while he was able to bring about this formation of 

 antitoxine in old crocodiles by keeping the reptiles at a tem- 

 perature of 30 C. 



Even then, however, he could not observe symptoms of illness 

 in the animals. Similar results were obtained by FERMI and 

 PERNOSSI in experiments on snakes, tritons, and turtle doves. 



Moreover, METSCHNIKOFF detected active tetanus toxine after 

 the lapse of a month in the livers of scorpions, in which there 

 had been neither symptoms of poisoning nor any formation of 

 antitoxine. 



The hen has been a particularly favourite subject for experi- 

 ments with tetanus poison, because although offering extreme 

 resistance she is not completely immune against it. METSCHNI- 

 KOFF asserts that the toxine can be recovered from the blood and 

 the ovaries, and that eventually slight traces of antitoxine appear. 

 ASAKAWA 2 found that the toxine introduced into hens' blood re- 

 mained almost unaltered until the seventh day, and then slowly 

 disappeared without being excreted. 



ASAKAWA could not detect any toxine in the brain or spinal 

 cord of the hen, although he found it in all the other tissues. 

 This may, of course, be due to the presence of blood in these 

 tissues leading to some erroneous conclusion as to presence of 

 toxine, while there is but little blood in the central nervous 

 system. But, on the other hand, it is also very probable that 

 slight traces of toxines disappear there by combining with 



1 Metschnikoff, "Influence de 1'organisme sur les toxines," Ann. Past., 

 xi., 801, 1897; xii., 81, 1898. Also, Immunitat, Germ, translation by 

 Meyer, p. 264. Jena, 1902. 



2 Asakawa, " Die Basis der natiirl. Immun. des Huhnes gegen Tetanus," 

 CentrcdU.f. Bakt., xxiv., 166, 1898. 



