260 SUSCEPTIBILITY AND IMMUNITY. 



during the sudden access of the fever, the spirilla are present in the blood in, 

 enormous numbers ; they all are free in the plasma, and not a single intra- 

 cellular spirillum is to be met with. During the apyretic stage (and in the 

 monkey this is, at the same time, the stage of resolution) not a single free spiril- 

 lum is discoverable in the blood, while the phagocytes of the spleen contain 

 the microbes. The like phenomena repeat themselves in all those cases where 

 it is possible to follow the fate of the microorganisms of acute disease during 

 the stage of recovery. Thus rats and pigeons very frequently survive an 

 attack of anthrax, and, where this occurs, the bacteria, which ,at the com- 

 mencement of the disease were for the most part free, now, during resolution, 

 are for the most part included within leucocytes and splenic phagocytes. 



Nor is this all. Analogous phenomena as a rule attend immunity, which 

 most often is but recovery in operation from the very onset of a disease 

 The more closely one studies this condition of immunity the more is one led 

 to the conviction that immunity and recovery are very intimately con- 

 nected ; that one can pass by slight gradations from the resolution of disease 

 to the production of immunity. So it is that, in inoculating refractory ani- 

 mals with the microbe to whose action they have been rendered immune, it 

 is found that the parasite begins to develop, but that from the onset a reac- 

 tion on the part of the organism shows itself, accompanied by a considerable 

 emigration of leucocytes, which soon include the bacteria in great numbers. 

 This relationship of phagocytosis to acquired immunity is in the highest 

 degree instructive. Where a given species of animal is specially sensitive 

 to the onslaught of one or other microorganism, there, during the course of 

 the disease, the phagocvtes are inoperative, including none, or almost none, 

 of the bacteria. On the other hand, when by previous vaccination these 

 animals have been rendered refractory, their phagocytes have acquired the 

 property of including the same bacteria. As an example of this I may cite 

 the action of the bacillus of anthrax and of the Vibrio Metschnikovi. In 

 ordinarv rabbits the development of anthrax is only followed by a very 

 feeble phagocytosis, while in vaccinated rabbits this phagocytosis is very ex- 

 tensive. Corresponding but yet more strongly marked differences are to be 

 made out between the unvaccinated guinea-pig an animal most readily 

 affected by the vibrionic septicaemia and the guinea-pig vaccinated against 

 the same; after inoculation with the Vibrio Metschnikovi none of the vibrios 

 are to be found in the cells of the former; in the latter the phagocytes are 

 simply replete with the microbes. 



The facts enumerated thus far would seem to prove that there exists a 

 certain antagonism between ihe microbes and the phagocytes, and this view 

 is confirmed by the fact that in general the microbes find the interior of the 

 phagocytes an unfavorable medium for their development and continued 

 existence. Very often it is possible to determine absolutely that the parasites 

 are killed within the phagocytes; after inoculating refractory animals with 

 bacteria, an afflux of white corpuscles toward the region of inoculation fol- 

 lowed by the inclusion of the bacteria and by their death, is seen to occur. 

 '-; >''-"> can be well followed where the anthrax bacilli are taken into 

 te phagocytes of animals that are, or have been rendered, immune They 

 occur also with a long series of other microorganisms studied in thisconnec- 

 tion, and, among others, m the case of the tubercle bacillus invading animals 

 that are more or less resistant. The giant cells of tuberculosis are, in fact 

 huge muUinuclear phagocytes, and here the intracellular destruction of the 

 the more clearly demonstrable, inasmuch as the microorganisms 

 >x In bit such very evident signs of degeneration; the bacilli swell their en- 

 veloping membrane becomes much thickened and highly refractive and in 

 imio the .content* lose their power of fixing the stain in* material so tint 

 eventually nothing is left Vut slightly yellowish form's rec^Whi pro- 

 !""!""'- ""! I"-"""', tlm Pillared burilli; ami ihrsr shadowy bodies unite 



r e rbet g ^^ 



