202 SUSCEPTIBILITY AND IMMUNITY. 



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

 be retained indefinitely within the blood vessels. On the other hand, 

 the passage of the tetanus antitoxine 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 recently (May, 1892) obtained experimental evi- 

 dence that the blood of vaccinated, and consequently immune, calves 

 contains something which neutralizes the specific virulence of vac- 

 cine 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 contact 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. 



The experimental evidence detailed gives strong support to the 

 view that acquired immunity depends upon the formation of 

 antitoxines in the bodies of immune animals. As secondary 

 factors it is probable that tolerance to the toxic products of patho- 

 genic bacteria and phagocytosis have considerable importance, but it 

 is evident that the principal role cannot be assigned to these agencies. 



PLATE IV. 



Fias. 1, 2, and 3. Leucocytes from the spleen of an inoculated monkey, 

 containing- Spirillum Obermeieri. (Soudake witch.) 



FIGS. 4 and 5. Leucocytes (" macrophages "') from a preparation of 

 muscle from a pigeon which succumbed to an anthrax inoculation. In Fig. 

 4 the bacilli are deeply stained ; in Fig. 5 they are pale. (Metschnikoff.) 



FIG. 6. Leucocyte from a frog seventy-two hours after the injection of 

 anthrax spores. (Trapeznikoff.) 



FIGS. 7 and 8. Leucocytes from a chicken four hours after the injection 

 of anthrax spores. (Trapeznikoff.) 



