126 Phylum Protozoa 



of Paramecia are 30 months of age. To this group I have recently fed 

 flour at approximately weekly intervals to determine whether dense 

 populations can still be produced. Four of the cultures now contain 

 an average concentration of 300 to 400 per cc. Such concentrations are 

 high for large cultures which are not evaporating. To the best of my 

 knowledge, none of these cultures has at any time contained a higher con- 

 centration. 



Reductions in length and number of Paramecia which are character- 

 istic of the declining culture are graphed in Fig. 44. The corresponding 

 increases which resulted when egg was fed are likewise indicated. 



SECURING CONCENTRATIONS 



These methods have been employed for concentrating either ro- 

 tifers or paramecia (Jones, 1932). There is reason to believe that a 

 considerable variety of protozoans and small metazoans will respond in 

 like fashion. 



Concentrations not needed for two days. Distribute cultures which 

 contain Paramecia among containers having the approximate dimensions 

 of quart fruit jars, filling each container half full. Add to each enough 

 freshly prepared, cooled infusion, made according to the formula given 

 above (variation is permissible), to fill it completely. Do not cover. 

 Within 40 to 60 hours the Paramecia will congregate on the sides of 

 the container at or immediately below the surface. Remove the con- 

 centration with a pipette having a finely drawn tip and a bulb. 



Concentrations for immediate use. Such concentrations may usually 

 be picked up directly from the bottom of an older culture, if a longer 

 pipette is employed. The Paramecia secured by such methods are usu- 

 ally smaller than those concentrated by the first method. 



Debris-free concentrations. Paramecia may be freed from the culture 

 debris by introducing into concentration tubes the animals and infusion 

 taken by either of the preceding methods. For this purpose I have em- 

 ployed glass tubes which were 30 cm. long and which had an internal 

 diameter of 8 mm. The organisms, following introduction, will settle 

 to the bottom, after which they will systematically migrate to the sur- 

 face, from which position they may be removed with a pipette. 



Bibliography 



Bauer, Frederick. 1926. Science 64:362. 



Butterfleld, C. T., Purdy, W. C, and Theriault, E. J. 1931. Pub. Health 



Repts. 46:393- 

 Dimitrowa, Ariadne. 1930. Arch. f. Protist. 72:554. 

 Glaser, R. W., and Coria, N. A. 1930. /. Exper. Med. 51 : 7S7. 

 Jennings, H. S., Lashley, K. S. 1914. J. Exper. Zool. 14:393. 

 Jones, Edgar P. 1930. Biol. Bull. 59:275. 

 1932. Science 75:52. 



