148 BACTERIAL POISONS. 



living germ or the germ-free culture. Pigeons and dogs 

 are but slightly susceptible to tetanus and they are made 

 still less so by being treated for a number of times with 

 small quantities of the virulent culture. After each re- 

 covery these animals are found to be less susceptible, and 

 finally they acquire a high degree of immunity, and then 

 their blood is employed in securing immunity in other 

 animals much after the manner already detailed for 

 anthrax. 



TI/ZONI and CATTANI have attempted to ascertain the 

 nature of that constituent of the blood-serum which gives 

 immunity. In these experiments serum from a dog which 

 had been rendered immune against tetanus was employed. 

 In the first place, a filtered culture of the tetanus germ 

 was concentrated in vacuo at 40 until one-half c.c. of 

 it would kill a rabbit within thirty-six hours. To this 

 amount of the culture, the blood-serum was added after 

 having been subjected to varied treatment, and the whole 

 was subsequently injected into a rabbit. The blood-serum 

 retains its antitoxic properties when kept in the dark at 

 15 for some days, and it may be heated to 60 without 

 injury. A temperature of 65 weakens, and one of 68 

 (the temperature at which the serum coagulates) completely 

 destroys the antitoxic properties of the serum. The 

 "tetanus-antitoxine" is non-diffusible. It is precipitated 

 from the blood-serum on the addition of absolute alcohol 

 and from the dried percipitate it may be extracted either 

 with water or glycerin, though very slowly with the 

 latter. From these facts it is concluded that the antitoxin 

 is a proteid with the characteristics of an enzyme. 



HANKIN gives the following argument in favor of the 

 theory that immunity is not due to ptomaines, but to pro- 

 teids : " It is generally admitted that in acquired immunity 

 against a disease we are dealing (for the most part, at least) 

 with a phenomenon of the nature of acquired tolerance of 

 a poison. If we consider what this theory really implies, 

 and, further, suppose that the poison involved is a pto- 

 maine or other body of an alkaloidal nature, numerous 

 difficulties immediately present themselves, For, in the 



