196 



BIOLOGY OF THE PROTOZOA 



throughout, while still others in the same organism are first acid 

 and then alkaline. Minchin (1912) suggests, in connection with 

 this diverse history of vacuoles in the same species, that different 

 food substances incite different responses on the part of the proto- 

 plasm much as different antibodies are formed from cells of the 

 Metazoa in response to toxins from different types of pathogenic 

 parasites. Shapiro (1927) followed the change in pH of the gastric 

 vacuole in Paramecium from an initial alkaline stage (7.6) which 

 quickly changed to a maximum acid stage (pH 4) from which it 

 slowly returned to the alkalinity of the surrounding water (pH 7). 

 In Heliozoa, Howland (1928) shows that the initial pH of a gastric 

 vacuole of Aciinosphacrium eichhornii is about neutral or slightly 



acid (pH 7 to 6.6). This lasts 

 for a period of five or ten min- 

 utes but changes to pH 4.3 ± 

 0.1 in all vacuoles in which 

 active digestion is going on, 

 while old vacuoles containing 

 indigestible remains have a pH 

 range from 5.4 to 5.6. 



In view of the number of 

 different ferments which have 

 been isolated from different 

 types of Protozoa, it is quite 

 probable that digestion does 

 not take the same course in 

 all types. Pepsin-like ferments, 

 which dissolve albumins in an 

 acid medium, were isolated by 

 Krukenberg (1886) from the 

 Mycetozoon Aethalium septi- 

 cum, and by Hartog and Dixon 

 (1893) from the ameba Pelo- 

 myxa pahisiris, while Metsch- 

 nikoff (1889) showed that 

 the food vacuoles in the Plas- 

 modia of Aethalium have an 

 acid reaction favorable to the activity of such ferments. Trypsin- 

 like ferments have likewise been isolated by Mouton (1902), from 

 soil amebae cultivated in large numbers on agar; also diastatic fer- 

 ments were easily obtained from Balautidium coli by Glaessner 

 (1908), and from Pelomyxa palustris by Hartog and Dixon (1893). 

 The typical course oi' a gastric vacuole through the endoplasm 

 of ciliates has been carefully worked out by Greenwood and by 

 Nirenstein for Carchesium and Paramecium caudatum (Fig. 102). 

 Prowazek (1897) staining with neutral red found a collection of red 

 granules about the gastric vacuole; similar granules were observed 



Fig. 102. — Carchesium polypinum ? 

 History of food vacuole; (c) stage of stor- 

 age and little change; (b) stage of acid 

 reaction; (c) neutral reaction. (After 

 Greenwood.) 



