422 GEO. T. HARGITT AND WALTER W. FRAY 



the hay infusion. More especially we have collected some data 

 on the growth of Paramecium in pure cultures of known bac- 

 teria. The work has been most rigidly controlled by checks and 

 teists at all times, which enables us to say that in our experi- 

 ments the food has been positively known and no foreign bac- 

 teria have gained entrance to the experimental cultures. 



The data covering the growth of Paramecium are not so 

 extensive as might be desired but certain conclusions seem to 

 be warranted. The technic of the cultures also appears to be 

 of sufficient value to merit attention. Since circumstances have 

 compelled a termination of these experiments for an indefinite 

 time it seems well to set forth the methods employed and the 

 results obtained. 



Our thanks are due to Prof. Henry N. Jones of the Depart- 

 ment of Bacteriology for the facilities in material and apparatus 

 placed at our disposal in working out the bacteriological part 

 of the investigation. 



HISTORICAL REVIEW 



The classic investigations of Maupas ('88) were the most ex- 

 tensive and carefully worked out of the earlier attempts to 

 understand the reproductive activities of infusoria. In his paper 

 an account is given of the methods employed, and while these 

 have been considerably modified by later workers they still are 

 of some importance. Among ^nore recent workers Calkins ('02 a) 

 was the first to undertake a careful study of the growth of 

 Paramecium under known conditions and with controlled factors. 

 This paper gives a detailed explanation of the method of mak- 

 ing hay infusions, methods of cultivation of the animals on 

 depression slides, and the like. Calkins' chief modification of 

 the earlier methods of study lay especially in growing Para- 

 mecium in depression slides with small amounts of liquid, and 

 their isolation each day to prevent conj ugation. 



As a criterion of the favorableness of the culture media, and 

 as an indication of the rate of growth and metabolism Calkins 

 ('02 b) used the rate of fission. ''The division-rate is taken as 

 the measure of vitality, for it represents the rate of metabolism, 



