14 Chapter I 



the vacuoles become brownish and then completely lose their colour. 

 This reaction, easily demonstrated, indicates that neutralisation of the 

 acid of the vacuoles by the protoplasm and the surrounding water, 

 both of which are alkaline in reaction, has taken place. 



In a medium distinctly acid the Infusoria digest their prey which, 

 in a very great number of cases, consists of Bacteria. These micro- 

 organisms are swallowed and carried into the digestive endoplasm 

 in the living condition ; we have evidence of this in the active 

 movements of a certain number of the bacteria ; at first they are 

 found isolated in the interior of the vacuoles, but later they collect 

 into more or less compact clumps. These masses of micro-organisms 

 undergoing digestion, when treated with neutral red assume a very 

 deep rose tint, preserving their bacillary form to the end, that is to 

 say up to the extrusion of the effete or waste material. There is, 

 indeed, only very imperfect dissolution not only of the bacilli as a 

 whole but also of their contents. Paramaecia placed amongst 

 cholera vibrios swallow them greedily and in great numbers, 

 digesting them as they would any other micro-organism. I have 

 never been able to see any conversion of vibrios into granules going 

 on within the digestive vacuoles. 



All the attempts that have been made in my laboratory to extract 

 a digestive fluid from Paramaecia have failed entirely. Very 

 large quantities of these Infusoria, obtained by filtration of rich 

 cultures, and macerated by different methods, have proved inactive 

 even in the case of those Bacteria which constitute their normal food. 



Intracellular digestion in the Infusoria unquestionably takes 

 place as the result of the action of some diastase ; but from the 

 impossibility of observing the action in vitro the properties of this 

 Diastase, except that it can act in a distinctly acid medium, cannot be 

 determined. 



Even less is known concerning the digestion of Rhizopods than 

 concerning that of Infusoria. It has long been recognised that, 

 in the majority of cases, Amoeba, Actmophrys and Rhizopods in 

 general, absorb a nourishment composed of lower plants and 

 animals, which are taken into the protoplasmic body by means of 

 the movements of amoeboid processes, pseudopodia or lobopodia. 

 [17] Once within the Rhizopod the nutritive particles are surrounded 

 by a digestive fluid, in which the presence of acid, may be recog- 

 nised by means of colour reactions. The addition of a drop of 

 Ehrlich's neutral-red to Amoebae in the act of digesting Bacteria 



