PHYSIOLOGY 



89 



(1881) examined the staining reactions of amoebae by means of 

 haematoxylin, and found that the watery vacuoles contained an 

 acid. Metschnikoff (1889) also showed that there appears an acid 

 secretion around the ingested litmus grains in Mycetozoa. Green- 

 wood and Saunders (1884) found in Carchesium that ingestion of food 

 particles stimulated the cytoplasm to secrete a mineral acid (Fig. 

 35). 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 



cv 



Fig. 36. Diagram showing changes in reactions in food-vacuoles of 

 Paramecium caudatum, after ingesting litmus (Shapiro), b, blue; cv, con- 

 tractile vacuole; lb, light blue; Ir, light red; r, red. 



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 



