90 PROTOZOOLOGY 



found in tlie food vacuoles of Paramecium, besides acid-alkaline 

 reaction change, that some vacuoles never show acid reaction and 

 others occasionally show sustained acid reaction. According to 

 Shapiro (1927), who observed reaction change of the food vacu- 

 oles in Paramecium caudatum (Fig. 35) by using phenol red, neu- 

 tral red, Congo red, and litmus, when the organism is kept in a 

 medium with pH 7, its food vacuoles are first alkaline (pH 7.6), 

 soon reach a maximum acidity (pH 4.0), while still in the poste- 

 rior half of the body. Later, the vacuoles show a decreased acidity, 

 finally reaching pH 7.0 prior to excretion. In Vorticella sp. and 

 Stylonychia pustulata, the range of pH observed in the food vacu- 

 oles was said to be 4.5-7.0 and 4.8-7.0 respectively. The food 

 vacuoles of Actinosphaerium, according to Rowland (1928), pos- 

 sess at the beginning pH 6.0-7.0 for 5 to 10 minutes, but this soon 

 changes to acid (pH 4.3) in which digestion appears to be carried 

 on. In older food vacuoles which are of less acid (pH 5.4-5.6), the 

 digestion appears to be at an end. 



Just exactly what processes take place in the food vacuole have 

 been observed only in a few cases. Nirenstein noticed the appear- 

 ance of numerous neutral red-stainable granules around the food 

 vacuole which pass into the inside of the vacuole, and regarded 

 them as carriers of a tryptic ferment, while Roskin and Levinsohn 

 demonstrated the oxidase reaction in these granules. A number of 

 enzymes have been reported in the Protozoa, some of which are 

 mentioned on page 91. 



These findings suffice to indicate that the digestion in Protozoa 

 is carried on also by enzymes and its course appears to vary 

 among different Protozoa. The albuminous substances are di- 

 gested and decomposed into simpler compounds by enzymes and 

 absorbed by the surrounding cytoplasm. The power to digest 

 starch into soluble sugars is widely found among various Protozoa. 

 It has been reported in Mycetozoa, Foraminifera, Pelomyxa, 

 Amoeba, Entamoeba, Ophryoscolecidae and other ciliates by sev- 

 eral investigators. In Pelomyxa, Stole (1900) found that the so- 

 called refractile bodies are intimately associated with the carbo- 

 hydrate metabolism in that they are filled with glycogen which 

 amount is proportionate to the food matter the organism ob- 

 tains. 



The members of Vampyrella (p. 291) are known to dissolve the 

 cellulose wall of algae, especially Spirogyra in order to feed on 



