76 BIOLOGY OF THE PROTOZOA 



in part, by the observations of Joyet-Lavergne (1927) on the differ- 

 ences in number, size, and staining capacity of the mitochondria in 

 the two individuals forming a syzygy in gregarines, thus indicating 

 what he interprets as male and female differentiation. 



Numerous observers have maintained that mitochondria are 

 responsible for digestive processes in the cell. The best evidence 

 in support of this suggestion has been furnished by Horning (1928), 

 who, using dark-field illumination, observed mitochondria of hetero- 

 trich ciliates adhere to food particles which had been recently 

 ingested; the mitochondria were included in the gastric vacuoles, 

 where they disappeared pari passu with the breakdown of the food 

 substances. Horning concludes that, among other possible func- 

 tions, mitochondria are direct agents in food hydrolysis, playing 

 the part of zymogen granules in the preparation of proteolytic 

 digestive ferments. Causey (1925-1926, etc.) likewise associates 

 mitochondria with food digestion, but he distinguishes between 

 spherical and rod-like forms, the latter being found clustered about 

 the gastric vacuoles (Endomoeba gingivalis) while the former are 

 distributed about the cell, where they act as centers of katabolic 

 activity (?). The difficulty of distinguishing between mitochondria 

 and bacteria is obvious, particularly when inside a gastric vacuole, 

 and this has been the main criticism directed against Homing's 

 interpretation, who meets it by describing the stain used which 

 was specific for bacteria and did not stain the mitochondria. 



Still other interpretations of the functions of mitochondria have 

 been advocated more or less vigorously by different observers. As 

 active centers they have been associated with the formation of 

 plastids (e. g., leucoplasts, pyrenoids, etc.) filamentous structures 

 of various kinds and with practically all of the cytoplasmic elements 

 of the derived organization. Cowdry (1924) states that more than 

 eighty substances have been claimed to come from mitochondria 

 (see especially Causey, 1926). Not only in cell activities have they 

 been regarded as direct causes, but also as latent or static centers 

 they have been interpreted as cytoplasmic transmitting agents in 

 heredity. 



None of the suggested interpretations mentioned above seems to 

 be adequate to explain the purpose of mitochondria. Their universal 

 distribution in Protozoa and in Metazoa indicates some important, 

 possibly fundamental activity which is closely bound up with life 

 of the cell or protoplasm in action. Kingsbury (1912) long since 

 suggested that mitochondria might be associated with cell respira- 

 tion, a suggestion adopted and enlarged by Joyet-Lavergne (1927) 

 mainly from study of gregarines and coccidia. According to this 

 observer there is a close connection between mitochondria in 

 coccidia and the catalyst glutathion which is a powerful oxidase. 

 (See Needham and Needham, 1926; Tunnicliffe, 1926; etc.) He 



