252 SUSCEPTIBILITY AND IMMUNITY. . 



in refractory ; so, with regard to the anthrax bacilli, in the very sensitive 

 rabbit the bactericidal properties of the humors are more pronounced than 

 they are in the refractory dog ; and Behring and Nissen, the two who al- 

 most simultaneously first drew our attention to these phenomena, in their 

 combined research, recently published, admit that, as against the bacteria 

 of anthrax, pneumonia, and diphtheria, this bactericidal property exists to 

 the same degree in the juices of animals of the same species, whether they 

 be susceptible or have been rendered immune. Often, again, it has been 

 determined that the blood removed from the organism has a greater power 

 of destroying bacteria than it has within the organism. A small quantity 

 of blood withdrawn from the body will, in certain instances, kill a mass of 

 bacilli greater than that which, injected into the circulation, would inevi- 

 tably cause death. Evidently, therefore, in this bactericidal influence extra- 

 vascular phenomena enact an important role phenomena, that is, which 

 have no connection with what occurs in the living refractory organism. 



From another point of view strong arguments have been directed against 

 this theory of the tissue fluids. It has been shown, especially by the re- 

 searches of M. Haffkine, that the death of the bacteria transported into or- 

 ganic fluids is largely due to the sudden change of medium, and that, in 

 passing from one medium to another by successive slight modifications in 

 the fluid of growth, it is easy to make bacteria live in fluids which, when 

 the change of environment has been abrupt, swiftly lead to their destruc- 

 tion. 



In order to gain an idea as to the part played in the refractory animal by 

 the fluids and the phagocytes respectively, the endeavor has been made to 

 separate the two by placing under the skin of frogs (which are naturally 

 immune to anthrax) minute packets formed of filter paper or of animal 

 membrane, and containing the bacilli. The paper, while permitting the 

 passage of fluid, wards off the wandering amoeboid cells for a certain time. 

 Shielded in this way from the phagocytes, though exposed to the action of 

 the juices, the bacilli grow well and produce the characteristic felted mass 

 of anthrax filaments. Baumgarten has not been able to confirm this experi- 

 ment, but Hueppe and Lubarsch have repeatedly verified it. 



But it is not even necessary to take these precautions in order to assure 

 one's self that anthrax spores germinate in the juices of refractory animals. 

 Recently, for instance, M. Trapeznikotf has found that, when these spores 

 are injected into the dorsal lymph sac of the frog, they constantly tend to 

 develop into bacilli, whose further growth is stopped by the phagocytes, 

 which include them, along with such spores as have not had lime to germi- 

 nate. Eventually the bacilli so absorbed are digested by their hosts, while 

 the included spores remain intact, although incapable of giving birth to 

 bacilli for so long a time as the phagocytes remain alive. And I might ad- 

 duce other similar cases. Such a comparative examination proves that in 

 the living body the bactericidal property resides in the phagocytes and not 

 in the fluids. 



Still, it may be urged that possibly these cells, which can thus devour and 

 destroy the living microbes, are only in a position to attack bacteria whose 

 virulence has already been lessened by other means. Were this so, the mi- 

 crobes present in a refractory organism should behave, not like parasites, 

 but as simple, inoffensive saprophytes. Hence these microbes powerless 

 to produce upon a refractory soil the toxic substances which render them 

 pathogenic and dangerous should easily be included and destroyed; so 

 that, according to this hypothesis, which "has frequently been brought for- 

 ward, the phagocytes play a purely secondary and dependent part, waiting 

 until the microbes are weakened before they seize upon them. In favor of 

 this view the fact has been cited that certain microorganisms cultivated in 

 the blood, or serum, of vaccinated animals become attenuated, so that they 

 no longer induce a fatal disease. The Bacillus anthracis grown in the blood 

 of vaccinated sheep no longer kills rabbits, and, according to Roger, the 

 Streptococcus erysipelatos grown in the blood of vaccinated rabbits only 



