\PreKminary remarks on immunity in animal kingdom 57 



digestive cells of the mesenterial filaments, can, however, also be 

 retained by other elements, amongst others, the cells of the ectoderm. 



As the digestion of the food-particles goes on within the ento- 

 dermic cells of the mesenterial filaments and as these organs can 

 easily be isolated from the rest of the Actinian, Mesnil was able to 

 study with great precision and care the phenomena of digestion 

 outside the organism. With this object he prej^ared extracts of the 

 filaments in sea-water and studied their action on various nutritive 

 substances. He confirmed the discovery of a soluble ferment made 

 by Leon Fredericq and demonstrated that it is capable of digesting 

 albuminoid substances (fibrin, coagulated albumen) in media which 

 are neutral, slightly alkaline or weakly acid. In this respect the 

 actino-diastase (the name given by Mesnil to the soluble ferment 

 of the Actinians) approaches most nearly to papain. On the other 

 hand, it is distinguished by its greater sensitiveness to an excess 

 of acid and also by its more powerful action on coagulated albumen. 



The actino-diastase acts vigorously at any temperature between 

 15° and 20° C, but the optimum temperature for its digestive action 

 is between 36° and 45° C. Higher temperatures weaken the diastatic 

 power, and heating to 55 — 60° C. inliibits it completely. Among the 

 products of the digestion of albuminoids by actino-diastase, Mesnil, 

 like his predecessors, found not only a notable quantity of peptone 

 but also products of the disintegration of the albuminoid molecule, 

 such as tyrosin and proteino-chromogen. Consequently actino- 

 diastase resembles Mouton's amoebo-diastase in certain respects. 



The nucleated red blood corpuscles of the low^er Vertebrata are 

 very convenient objects on which to observe the process of intracellular 

 digestion within the cells of the mesenterial filaments. Mesnil has also 

 studied them in vitro under the influence of actino-diastase. Under 

 these conditions the phenomena of digestion recall very clearly those 

 that have been observed within the digestive cells. The oval red 

 corpuscles of the fowl and goose become spherical as a result of the 

 solvent action on their membrane, and the haemoglobin diffuses into 

 the fluid. The membranes and tlie nuclei of the corpuscles are, how- 

 ever, little altered and may be recognised under the microscope. The 

 difference between this and digestion within the cells reduces itself 

 to a more feeble digestive action of the aqueous extract. It is evident 

 that the preparation of this extract is only capable of bringing into [62] 

 prominence a certain proportion of the actino-diastase contained in 

 the entodermic cells of the filaments. 



