194 



BIOLOGY OF THE PROTOZOA 



in color according to the acid or alkaline nature of the fluids in 

 which they lie. The observations of le Dantec (1890), Fabre- 

 Domergue (1888), Metschnikoff (1889), Greenwood (1887-1894), 

 Nirenstein (1905), Khainsky (1910) and Metalnikoff (1903, 1912), 

 together with the study of extractives by Mesnil (1903), Mouton 

 (1902), Metschnikoff '(1893), Krukenberg (1886), Hartog and 

 Dixon (1893), etc., have given a fairly comprehensive idea of the 

 processes of intracellular protein digestion in Protozoa. Another 

 group of observers including Meissner, Greenwood and Saunders, 

 Stole (1900), Wortmann (1884), Celakowski (1892), Nirenstein, 

 etc., have shown the digestive possibilities in relation to carbo- 

 hydrates and fats. 



Fig. 101. — Colpidium colpoda and Paramecium aurelia after feeding with amylo- 

 dextrin and treatment with iodide. (After Cosmovici, courtesy of Annales Scien- 

 tifique de l'Universite de Jassy.) 



An interesting conception of the gastric vacuoles in ciliates has 

 been given recently by Cosmovici (1932). Using an ingenious 

 method of dissolving rice starch with saliva and immersing ciliates 

 in the dextrin thus formed, he found, upon treating them at differ- 

 ent intervals with iodide, that a canal, colored blue, often con- 

 voluted or swollen into "gastric vacuoles," runs from mouth to 

 anus (Fig. 101). Further investigation of this remarkable canalic- 

 ular system is needed. 



The majority of Protozoa which ingest "solid" food take in at 

 the same time more or less water, which forms the gastric vacuole. 

 Thus in trichostomatous ciliates a vacuole is formed at the base of 



