124 Phylum Protozoa 



fresh hay infusion, egg, chocolate, peptone solution, or milk as supple- 

 mental foods (Jones, 1933). Any simple method of introducing such 

 substances is usually satisfactory if the materials are in a finely divided 

 state or a fluid condition. Flour is introduced by sprinkling approxi- 

 mately y 2 gram upon the surface of 700 cc. of infusion in as unlumped a 

 condition as possible, and stirring. A solution of egg may be prepared 

 by breaking an egg into 100 cc. of distilled water in a flask, and shaking 

 with glass beads. Sterile technique may be employed, but I have not 

 observed that it materially alters the end result. 



Other investigators report temporary revival of declining cultures 

 secured by introducing sugar (McClendon, 1909), bread (Bauer, 1926), 

 or fresh hay infusion (Kudo, 193 1) ; and the culture has been maintained 

 for a year, in one instance (Kudo, 1934) by occasionally introducing a 

 few grains of wheat and a few pieces of timothy hay. 



The degree of success which may be had in maintaining mass-cultures 

 by feeding is indicated by the following preliminary report of the first 

 which I so tested. This was a 700 cc. culture, loosely covered, made in 

 accordance with the formula furnished above. Controls were initiated 

 in similar fashion. 



In the controls, which developed and declined in the usual mass- 

 culture fashion, Paramecia could be found for a period of approximately 

 six months. Dense populations were not present after the initial three 

 months. The fed culture maintained Paramecia for more than twenty 

 months. It produced a dense population when fed when fourteen months 

 old, although the Paramecium population had dropped almost to zero 

 while the culture had gone unfed over a summer's vacation which had 

 just preceded. The Paramecia eventually disappeared for no known 

 reason, other than that the culture had not been fed for some time. 



To further test the potential longevity of Paramecium cultures, four- 

 teen cultures of a capacity of one gallon were prepared. These received 

 infusion of approximately the same composition, and seed in the same 

 ration per volume as described above. They were seeded November 12, 

 1932. 



It became necessary to feed flour to all of these gallon cultures before 

 they were six months old, because, in every culture the Paramecium 

 population had declined almost to extinction. Six cultures now survive 

 (June, 1935). These cultures have been fed repeatedly, usually only 

 when the Paramecium populations were quite low, whereupon they have 

 characteristically produced larger populations. Flour has been most 

 frequently fed, but milk, glucose, albumin, and ethyl alcohol have been 

 used at times. An epidemic of mold which destroyed the Paramecia 

 appeared in practically every culture to which ethyl alcohol was fed. 



At the present time, the six of the series which now retain populations 



