90 MARY H. CHAMBERS. 



CONCLUSIONS. 



As a food hormone, potato extract apparently has little effect 

 on the division rate of Paramecium. The influence of yeast is 

 evident as exemplified in Tables III. and IV., i. e., it increases 

 the division rate. 



In the comparative study of the four races the influence of 

 yeast is not evident. Both control and experimental lines 

 respond with increased division rate if the Paramecia have pre- 

 viously been in a starved condition. If food has been plentiful 

 the rich diet of malted milk and yeast seems to have little effect. 



Contrasting results were obtained with pituitary solution 

 added to the hay infusion and malted milk basic substances. 

 Suprarenal extract added to the basic fluid in which the Para- 

 mecia lived, caused an increase in the rate of division. 



This experiment is to be considered as an indicator only. It 

 was undertaken with the point in mind that if these solutions 

 influenced the division rate of Paramecia a more extensive work 

 would follow, i. e., the bacterial content would be taken into 

 consideration. It has been a generally accepted fact that the 

 normal diet of Paramecium is composed of various kinds of 

 bacteria and that in their absence growth does not take place, 

 and even maintenance is impossible. In 1908 Jennings said, 

 'To make the conditions of existence the same, it is not sufficient 

 to attend merely to the basic fluid, the bacteria must also be the 

 same." 



Hargitt and Fray (1917) elaborated on previous methods of 

 determining the bacterial content and they proved that Para- 

 mecium can live in media which have undergone sterilization 

 provided at least one sort of bacteria remains in the culture. 



LITERATURE. 

 Buddington, R. A. 



'15 Division Rate in Ciliate Protozoa as Influenced by Thyroid Constituents. 



BIOL. BULL., Vol. 28, p. 304. 

 Calkins, Gary N. 

 '02 Studies on the Life History of Protozoa. Arch. f. Ent. Mech., Vol. 15, 



PP- 139-186. 

 Funk, C., and Macallura, A. B. 



'15 The Action of Yeast Fractions on the Growth of Rats. Jour. Biol. Chem., 

 Vol. 23, p. 63. 



