PROTECTIVE INOCULATIONS. 355 



trate from a virulent culture with blood serum from an immune animal 

 and allowing it to stand for twenty -four hours; a dose three hundred 

 times greater than would have sufficed to kill a mouse proved to be 

 without effect after such admixtures with blood serum; as before 

 stated, the blood serum of animals which are not immune has no 

 effect upon the poison. The duration of immunity induced in this 

 way was from forty to fifty days. Blood serum from an immune rab- 

 bit, preserved in a cool, dark room, retains its power of neutralizing 

 the tetanus poison for about a week, after which time it gradually 

 loses it. Having found that chickens have a natural immunity against 

 tetanus, Kitasato made experiments to ascertain whether their blood 

 serum would also neutralize the tetanus poison ; the result was nega- 

 tive. 



That the tetanus poison is present in the blood of individuals who 

 die from tetanus has been proved by Kitasato by injecting a small 

 quantity (0.2 to 0.3 cubic centimetre) of blood from the heart of a 

 fresh cadaver into mice; the animals develop typical tetanic symp- 

 toms and die in from twenty hours to three days. 



Tizzoni and Cattani have (1891) reported results similar to those 

 obtain by Kitasato. By repeated inoculations with gradually in- 

 creasing doses of the tetanus poison they succeeded in making a dog 

 and two pigeons immune, and found that blood serum from this im- 

 mune dog, in very small amount, completely destroyed the toxic 

 power of a filtrate from cultures of the tetanus bacillus one to two 

 drops of serum neutralized 0.5 cubic centimetre of filtrate after fifteen 

 to twenty minutes' contact. They also ascertained that small amounts 

 of blood serum from this immune dog injected into other dogs or 

 white mice produced immunity in these animals; but they were not 

 able to produce immunity in guinea-pigs or rabbits by the same 

 method. 



In a later communication (May, 1891) Tizzoni and Cattani give 

 an account of their experiments made with a view to determining 

 the nature of the substance in the blood serum of an immune animal 

 which has the power of destroying the toxalbumin of tetanus " tet- 

 anus antitoxin." They found, in the first place, that this antitoxin 

 in blood serum is destroyed in half an hour by a temperature of 68 

 C. ; further, that it does not pass through a dialyzing membrane; that 

 it is destroyed by acids and alkalies. As a result of their researches 

 they conclude that it is an albuminous substance having the nature of 

 an enzyme. 



Yaillard has succeeded in producing immunity in rabbits by re- 

 peated injections into the circulation of filtered cultures in all twenty 



