DIGESTIVE PROCESSES IN PLANAlllJi. 
215 
It is now a generally recognised fact that intra-cellular 
digestion in Protozoa is accompanied by a secretion of acid 
in the vacuoles,, but witli regard to the part played by this 
acid in the process of digestion there is a large difference of 
opinion. 
(rreenwood and Saunders (’94) sliow that proteolysis com- 
mences when the acid reaction is over, and is replaced by a 
neutral reaction. That the vacuole fluid also contains a 
proteolytic enzyme there can be no donbt. 
IMouton (’02) succeeded in extracting from cultui-es of 
AmoebEe a diastase, chiefly of ei proteolytic action and 
approaching trypsin in its nature. This diastase he identified 
with the fluid in the interior of the digestive vacuoles. 
Nirenstein (’05j does not think that the acid in the 
vacuoles has anything to do with digestion, and Mouton has 
shown by a most carefid series of experiments that the 
ama'bo-diastase which he extracted from AnioebEe has a 
digestive action in an alkaline, neutral or faintly acid medium. 
On the other hand, Metschnikoff (‘ L’lmniunite ’), by feeding 
Planaria with blood with which had been mixed some grains 
of blue litmus, came to the conclusion that digestion in those 
animals takes phice in an sxcid medium. 
“ L’etude des planaires nous montre que la nourriture des 
ces animaux subit exclusiveinent la digestion intra-cellulaire, 
dans un milieu fsiibleinent acide et avec I’aide d’un ferment 
soluble. Pile nous fournit deja nne preuve de ce que la 
digestion intra-cellulaire typique est un processus chimiqne, 
du si I’intervention d’enzymes.” 
I have shown in connection with the absorption of fat 
that digestion in Planaria is not entirely intra-cellular, but 
the sudden change in the staining reaction of the ingested 
leucocytes is strong evidence in support of the view that the 
intra-celluhir digestion in these animals tsikes place in an 
acid medium. The chsinge in the staining reaction of the 
cytoplasm of the ingested leucocytes from the normal acid to 
the basic stains would seem to indicsite that the ingested 
material becomes impregnated by an acid fluid. 
