immunity against pathogenic micro-organisms 141 



weakening the bacillus, but rather by reinforcing the resisting power 

 of the organism. The low temperatures (6° — 10° C.) that are favour- 

 able to a fatal infection have a different action; that is to say, 

 they weaken the reaction of the inoculated frogs. 



Although Ernst has not studied the mechanism of this resistance 

 fully, it is evident, from the data he has supplied, that it consists in 

 a phagocytic reaction. He was able to demonstrate the ingestion of 

 the bacilli by the phagocytes in the susceptible refrigerated frogs, as 

 well as in the refractory frogs, kept at a higher temperature ; but in 

 the former case the phagocytosis was so feeble that 24 hours after 

 inoculation a considerable number of fi'ee bacilli were still found 

 in the lymph of the dorsal sac, whilst in the refi*actory frogs the 

 much more active phagocytosis brought about the disappearance of 

 the free bacilli during the first day. If, as is very probable, the 

 analogy of this septicaemia with anthrax in frogs, upon which Ernst 

 insists, really exists, it must be concluded that the susceptibility of [iso] 

 these Batrachians to the modified race of the bacillus depends on 

 their weak phagocytic resistance. 



Since, in these two examples of natural immunity in the frog, we 

 have seen that the phagocytic activity exhibits itself in an active 

 form against bacteria which readily develop in the fluids of the 

 same animal, we might conclude that the reaction of the phagocytes 

 constitutes a general mode of defence in cold-blooded animals. 

 But Lubarsch^, a very cautious observer, has expressed an opposite 

 view, based on his studies on the bacillus of mouse septicaemia. 

 He convinced himself that frogs will resist injections of even con- 

 siderable quantities of this bacillus, without any co-operation on 

 the part of the phagocytes. As we have, here, to do with a 

 matter of fact, Mesnil {I.e.) set himself to verify these observations, 

 with the object of establishing whether it was a case of a real 

 exception or of a simple misunderstanding. He was able to de- 

 monstrate, by irrefutable observations and experiments, that the 

 bacilli of mouse septicaemia when inoculated into frogs, set up a 

 very pronounced positive chemiotaxis on the part of the phagocytes, 

 which seized and digested the bacilli just as they do the anthrax 

 bacillus. This apparent exception, therefore, becomes transformed 



^ Centralbl. f. Bakteriol u. Parasitenk., Jena, 1889, Bd. vi, SS. 481 and 529; 

 Fortschr. d. Med., Berlin, 1890, Bd. viii, S. 665; Ztschr. f. klin. Med., Berlin, 1891 ; 

 " Ueber Immunitat u. Schiitzimpfung," Schneidemiihrs Thiermed. Vortrdge, 1892, 

 Bd. II. 



