Acquired immunity against micro-organisms 273 



normal serums exercise their protective action although they contain 

 no fixative. This follows from Bordet and Gengou's experiments 

 already described, according to which the cytases, placed in contact 

 with micro-organisms in normal serums, remain free, simply because 

 of the absence of fixatives. 



We are led, then, from these demonstrations to recognise the 

 presence of stimulins not only in specific serums, but also in normal 

 serums. Between the two there is this difference that, when applied 

 with the normal fluids, the stimulins alone act, whilst when injected 

 with the serum of the animal enjoying acquired immunity the action 

 of the stimulins is facilitated and reinforced by the fixatives or 

 sometimes, perhaps, by the agglutinins. 



The stimulating influence of certain normal serums may be so 

 considerable that it may prevent infection by the micro-organism, 

 injected at the same time in a dose many times more than lethal. 

 Wassermann 1 protected guinea-pigs by injecting into the peritoneal [287] 

 cavity a quantity as great as 40 times the lethal dose of typhoid 

 bacilli, by introducing at the same time and at the same place 3 c.c. 

 of normal rabbit's serum, heated to 60 C. Besredka 2 , who confirmed 

 this observation, has analysed its special mechanism. He showed 

 that the serum exercises a very marked stimulating influence on 

 the guinea-pig's leucocytes, which then exhibit a truly extraordinary 

 phagocytic activity. They are seen to act in the peritoneal fluid, 

 but they are much more active in the region of the omentum, where 

 the leucocytes gorge themselves with micro-organisms, devouring 

 them by dozens. The stimulating action of the heated rabbit's serum 

 is exercised in a similar fashion if, instead of micro-organisms, grains 

 of carmine be injected. Very shortly after the commencement of 

 the experiment very little carmine is found outside the cells ; it is 

 all either ingested by individual leucocytes, if the grains are small, 

 or surrounded by numerous leucocytes when the grains are massed 

 together ; this phagocytosis is most developed in the region of the 

 omentum, exactly as in the case of typhoid bacilli. 



These facts, which so clearly demonstrate the stimulating action 

 of the normal rabbit's serum, prove in another way that the stimulin 

 resists heating to 60 C., and that, in this respect, it resembles the 

 agglutinins and fixatives. This may afford us an indication as to the 

 nature of the stimulating substance. The possibility of obtaining an 



1 Deutsche med. Wchnschr., Leipzig, 1901, S. 4. 



2 Ann. de VInst. Pasteur, Paris, 1901, t. XY, p. 209. 



B. 18 



