354 SUSCEPTIBILITY AND IMMUNITY. 



leucocytes, which, instead of being attracted by the bacterial products, are 

 repelled ; where the animal is vaccinated or refractory a much slighter in- 

 flammation is sufficient to produce an abundant emigration of the leu- 

 cocytes. 



Recently Behring has brought forward another view which would ex- 

 plain immunity in a wholly different way. According to him, the bac- 

 teria can live, and even preserve their virulence, in the refractory organism, 

 but the toxines excreted, by them now undergo a modification so as to be 

 rendered completely inoffensive for the animal. And to this "toxicide 

 property " of the organism is to be attributed the essential quality of the 

 immune state. It is impossible to pronounce upon the arguments that have 

 led up to this theory, for as yet they have not been circumstantially set 

 forth ; but already one can declare that such a theory is in no wise applicable 

 to the phenomena of immunity in general. In three diseases remarkable 

 for their pronounced toxic character vibrionic septicaemia, pyocyanic dis- 

 ease, and hog cholera affecting the rabbit as shown by the experiments of 

 Charrin, Gamaleia, and Selander, the toxines are so little attacked by the re- 

 fractory organism that the same quantity of these substances (freed from 

 bacteria) suffices to kill an animal very susceptible to one or other disease, 

 and an animal vaccinated against it and thus completely immune. So, too, 

 non-fatal doses of these toxines produce in animals of the two categories the 

 same febrile and inflammatory reactions. The proof is clear that there is no 

 special destruction of toxines in the refractory animal, and that the "toxicide 

 property," if it exists, is not one whit more developed after vaccination than 

 before. Passing in review all these counter theories, we see that each of 

 them can only be applied to a certain number of facts ; in some an attenu- 

 ating or even bactericidal influence of the juices is relied upon, in others an 

 anti-inflammatory action, in yet others a toxicide property. Still the pha- 

 gocytic reaction is the only constant in all those cases of immunity and 

 recovery that have as yet been sufficiently studied, and while certain of the 

 factors mentioned (the attenuating and toxicide properties) do not in the 

 least touch upon the continued existence or otherwise of the microorganism, 

 the bactericidal power of the phagocyte puts an end to the parasite itself, and 

 thus at a given moment prevents further manifestation of its virulence, or 

 preserves the animal attacked at a time when the toxicide properties would be 

 found wanting, arid the microbe remaining alive would consequently gain 

 the upper hand. 



But while thus placing before you the important part played by the pha- 

 gocytes, I do not wish it to be thought that these cells are unaided in their 

 contest by other defensive means possessed by the organism. This is far 

 from being my view. Thus, in the febrile reaction, we see a puissant auxil- 

 iary very definitely favoring the work of the phagocytes. This febrile re- 

 action has only to be inhibited as was done by M. Pasteur in the anthrax 

 of fowls and animals naturally refractory to the affection succumb to the 

 ravages of the bacilli. It is not possible at the present time to state fully 

 and accurately all these influences which are associated in aiding phago- 

 cytic action, but already we have the right to maintain that, in the prop- 

 erty of its amoeboid cells to include and to destroy microorganisms, the 

 animal body possesses a formidable means of resistance and defence 

 ajainst these infectious agents. 1 



We are disposed to agree with Metschnikoff in his final conclu- 

 sion, as above stated in italics. But in view of experimental evi- 

 dence, to be referred to later, we cannot accept the so-called Metsch- 

 nikoff theory as a sufficient explanation for the facts relating to 

 natural and acquired immunity in general, and must regard phago- 

 cytosis simply as a factor which, in certain infectious diseases, ap- 

 1 From the British Medical Journal. 



