PHYSIOLOGY 



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food particles stimulated the cytoplasm to secrete a mineral acid. 

 According to Nirenstein (1925), the food vacuole in Paramecium 

 undergoes change in reaction which can be grouped in two periods. 

 The first is acid reaction and the second alkaline reaction, in which 

 albumin digestion takes place. On the other hand, Khainsky (1910) 

 observed that the food vacuole of ciliates, such as Paramecium, is 



Fig. 37. Diagrams showing movements of food vacuoles in Vorticella 

 sp. (Hall and Dunihue). a, diagram of the migration paths of six food 

 vacuoles (vacuoles 1, 2, most recently formed; 3, 4, recently formed; 5, 6, 

 formed some time before) ; b-d, stages in extrusion of a food vacuole (b, 

 food vacuole entering gullet; c, a later stage; d, the food vacuole leaving 

 cytostome, while another one is moving up toward the cytopyge). 



acid during the entire period of protein digestion, and becomes neu- 

 tral to finally alkaline when the solution of the food substance is 

 ended. Metalnikoff (1912) found that in the food vacuoles of Para- 

 mecium, besides acid-alkaline reaction change, some vacuoles never 

 show acid reaction and others occasionally show sustained acid reac- 

 tion. Shapiro (1927) studied the reaction change of the food vacuoles 

 in Paramecium caudatum by using phenol red, neutral red, Congo 

 red, and litmus, and found that 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 posterior 



