266 SUSCEPTIBILITY AND IMMUNITY. 



covery from an attack of an acute infectious disease. But the idea 

 that during such an attack an antidote to the disease poison is de- 

 veloped in the tissues is yet so novel, and the experimental evidence 

 in support of this view is of such recent date, that it would be pre- 

 mature to accept this explanation as applying to immunity in gene- 

 ral. It seems difficult to believe that a'n individual who has passed 

 through attacks of measles, mumps, whooping cough, scarlet fever, 

 small-pox, etc., has in his blood or tissues a store of the antitoxin of 

 each of these diseases, formed during the attack and retained during 

 the remainder of his life, or continuously produced so long as the 

 immunity lasts. Moreover, in those diseases to which the experi- 

 mental evidence above recorded relates diphtheria, tetanus, pneu- 

 monia as they occur in man, no lasting immunity has been shown 

 to result from a single attack, and in this regard they do not come 

 into the same class with the eruptive fevers and other diseases in 

 which a single attack usually protects during the lifetime of the in- 

 dividual. 



In those instances in which acquired immunity has been shown 

 to be due to the production in the body of the immune animal of an 

 antitoxin, it is still uncertain whether there is a continuous produc- 

 tion of the protective proteid, or whether that formed during the 

 attack remains in the body during the subsequent immunity. The 

 latter supposition appears at first thought improbable ; but when we 

 remember that the protective proteids which have been isolated by 

 Hankin from the blood and spleen of rats, and by Tizzoni and Cat- 

 tani from the blood of animals made immune against tetanus^ do 

 not dialyze, it does not seem impossible that these substances might 

 be retained indefimtely'within the blood-vessels. On the other hand, 

 the passage of the tetanus antitoxin into the mother's milk, as 

 shown by Ehrlich's experiments upon mice, indicates a continuous 

 supply, otherwise the immunity of the mother would soon be lost. 



The writer has obtained (May, 1892) experimental evidence that 

 the blood of vaccinated, and consequently immune, calves contains 

 something which neutralizes the specific virulence of vaccine virus, 

 both bovine and humanized. Four drops of blood serum from a calf 

 which had been vaccinated two weeks previously, mixed with one 

 drop of liquid lymph recently collected in a capillary tube, after con- 

 tact for one hour was used to vaccinate a calf ; the same animal was 

 also vaccinated with lymph, preserved on three quills, which was 

 mixed with four drops of serum from the immune calf and left for 

 one hour. The result of these vaccinations was entirely negative, 

 while vaccinations upon the same calf made with virus from the 

 same source, and mixed with the same amount of blood serum from 

 a non-immune calf, gave a completely successful and typical result. 



