134 Chapter VI 



a great number of bacilli belonging to the group of Bacillus subtilis. 

 He observed that when injected into the body of the cricket these 

 bacilli are devoured and destroyed by the leucocytes of the blood 

 and by the large cells of the pericardial tissue corresponding to the 

 elements of the spleens of Kovalevsky. Whilst the crickets and other 

 Orthoptera, which are rich in phagocytes, exhibit a real immunity 

 against these bacilli, insects which have very few leucocytes such 

 as butterflies, flies and Hymenoptera are found to be much more 

 susceptible to infection by the same bacilli. In this case the direct 

 relation between immunity and phagocytosis is very marked. 



The Mollusca also furnish some interesting examples of natural 

 immunity. Karlinsky 1 has observed that anthrax bacilli, when in- 

 jected into the blood of slugs and snails, soon disappear from their 

 bodies ; these pulmonate Gasteropods are absolutely unaffected by 

 this bacillus so formidable for many species of animals. From the 

 rapidity of this disappearance of the bacilli it has even been con- 

 cluded that it was impossible for this bacillus to live in the fluids 

 of Mollusca. Kovalevsky (I.e. p. 443) has studied this question with 

 the carefulness that characterises all his work. He confirms the 

 fact that snails (Helix pomatia) resist the introduction of a large 

 quantity of anthrax bacilli into their bodies ; he notes also that 

 these bacteria disappear from the blood. But he finds them again 

 in the tissues of the foot, and especially in the cells which surround 

 the pulmonary vessels. "The greater number of the bacteria are 

 found in the cells of that part of the pulmonary region in Helix 

 which adjoins the heart and kidney. All the bacteria were ingested 

 by the cells and I easily succeeded in demonstrating this not only in 

 sections but also in bulk" (p. 444). The snails remained in good 

 health in spite of the presence in their phagocytes of numerous 

 bacteria which maintained themselves there for some time. At the 

 end of ten or twelve days and more these bacteria still presented 

 their usual aspect ; this accords well with the slowness with which 

 intracellular digestion goes on in the majority of the Irivertebrata. 

 These bacteria were, however, no longer living, although still un- 

 [143] digested. Morsels of the pulmonary tissue of the snails that were 

 injected with anthrax bacilli still gave cultures 48 hours after in- 

 jection and contained bacilli capable of giving fatal anthrax to mice. 

 Later, media seeded with similar particles remained sterile, and mice 

 inoculated therewith continued to live. From these experiments it may 

 1 Centralbl.f. Bakteriol. u. Parasitenk., Jena, 1889, Bd. v, S. 5. 



