Preliminary remarks on immunity in animal kingdom 55 



The epithelium of the mesenterial filaments is therefore the organ 

 of digestion in the Actinians. The nutritive parts of their prey pass 

 into the amoeboid epithelial cells and there undergo a purely intra- 

 cellular digestion. If we add to the shrimp-muscle or other food 

 a little carmine or blue litmus powder, the mesenterial filaments 

 ingest it also and become pigmented. After eating carmine they 

 assume a very brilliant rose colour (fig. 11) ; blue litmus colours them [59] 

 rose violet. This change of colour in the interior of the cells of the 

 filaments indicates a decidedly acid reaction of their contents 1 . When 

 one adds to the mesenterial filaments which are carrying on the process 

 of digestion a drop of a 1 / solution of neutral red they assume various 

 shades of red (fig. 12). 



This intracellular digestion in the Actinians has been confirmed 

 by several observers, amongst whom may 

 be cited Chapeaux 2 and Bjelooussoff 3 . 

 It has often been asserted, however, 

 that, along with a digestion in the in- 

 terior of the cells of the mesenterial 

 filaments, there is, in the Actinians, a 

 secretion in the coelenteric cavity of 



their body of fluids which digest nutri- FIG. 12. Portion of mesenterial 

 tive matter by means of a soluble filament of an Actinian, 



ferment. A ferment similar to trypsin ** ined with 10 '' neutral 



has been extracted from Actinians by 



Leon Fredericq and Krukenberg. But, in presence of contradictory 

 assertions, it remained undecided whether, in the enzymatic digestion, 

 this ferment does its work in the fluid of the coelenteric cavity or 

 whether it represents the active factor in intracellular digestion. 



With the object of definitely elucidating a problem of such general 

 importance, Mesnil, the superintendent of my laboratory, has been 

 good enough to carry out a fresh series of experiments on the digestion 

 of the Actinians and has studied this process not only in animals kept 

 in captivity in aquaria but also in Actinians living under natural con- 

 ditions in the sea 4 . 



As intracellular digestion is of interest to us specially in connection 

 with the resorption of formed elements in the tissues and cavities of 



1 Metchnikoff. Ann. de TInst. Pasteur, Paris, 1893, t. vn, p. 348. 



2 Bull. Acad. roy. de JBelg., Brux., 1893, t. xxv, p. 262, and Arch, de Zool exper., 

 Paris, 1893, 3 me serie, t I, p. 139. 



3 "Etudes de physiologic sur les Actinies," Charkoff, 1895 (in Russian). 



4 Ann. de VInst. Pasteur, Paris, 1901, t. xv, p. 352. 



