PHYSIOLOGY 



89 



Brandt (1881) examined the staining reactions of amoebae by 

 means of haematoxylin, and found that the watery vacuoles con- 

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

 an acid secretion around the ingested litmus grains in Myceto- 

 zoa. Greenwood and Saunders (1884) found in Carchesium that 

 ingestion of food particles stimulated the cytoplasm to secrete a 



cv 



cv 



Fig. 35. Diagram showing changes in reactions in food-vacuoks of 

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

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



mineral acid (Fig. 34). 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 sec- 

 ond 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 acid during the entire period of 

 protein digestion, and becomes neutral to finally alkaline when 

 the solution of the food substance is ended. Metalnikoff (1912) 



