SUSCEPTIBILITY AND IMMUNITY. . 249 



affections in which an. acute course is accompanied by considerable phago- 

 cytosis, the fatal termination is far from occurring- at the same early period 

 as in the diseases recorded above. Thus mouse septicaemia, characterized as 

 it is by frequent intracellular bacteria, has a duration in the mouse two and 

 a half times as long- as that of anthrax in the same animal. But in general a 

 well-marked phagocytosis is associated with diseases presenting an essen- 

 tially chronic development ; it is in affections such as tuberculosis, leprosy, 

 rhinoscleroma, glanders, that the specific bacteria are most readily taken up 

 by the phagocytes ; it is here that, at the seat of the disease, we meet with in- 

 numerable macrophages epithelioid cells in which lie the individual micro- 

 organisms. 



Further, if we consider the phenomena associated with the resolution of 

 an infectious disease, this in verse relationship between the malignancy of the 

 malady and the occurrence of phagocytosis is, if possible, yet more clearly 

 demonstrated. Notice, for instance, what obtains during the progress of re- 

 lapsing fever, a malady still fairly common in Russia and other Sclavonic 

 countries, and one which, while presenting many difficulties to the bacteri- 

 ologist, in that the specific spirochaete has so far resisted cultivation, and in 

 that it cannot be communicated to the ordinary animals of the laboratory, is 

 nevertheless in many respects not ill -adapted for our present purpose. Here v 

 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 #t 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 shoivs 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 phagocytes 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 

 ordinary 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 the microbes and the phagocytes, and this view 

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



