EFFECT OF EXCRETION PRODUCTS bF INFUSORIA 577 



The paramaecia used in this work were from my pedigreed 

 race of Paramaecium aureUa (I). This was at the 2800th genera- 

 tion in January, 1912, when the study was started and had 

 attained the 3450th generation by the conclusion of the experi- 

 ments in December of the same year. For the hypotrichous 

 forms which were employed I am indebted to Mr. George A. 

 Baitsell who supplied them from his pedigreed races. Emphasis 

 is placed on the fact that the animals which formed the subjects 

 of the experiments had been under observation for considerable 

 periods of time (in the case of the paramaecia, for five years) and 

 consequently their rate of reproduction and the exact conditions 

 to which they had been subjected before the experiments were 

 known. Further, since the pedigreed races were each originally 

 started with a single individual, all the specimens of the respective 

 species were 'sister' cells and therefore all the experiments were 

 made on the 'same protoplasm.' 



A weak extract of hay was employed as a culture medium, 

 which was made by boiling about 10 grams of hay in a liter of 

 water for five minutes. The hay was then immediately filtered 

 off and the liquid distributed equally in three flasks and allowed 

 to cool. About a dozen paramaecia and a dozen hypotrichs were 

 then isolated from their respective pedigreed cultures and allowed 

 to mingle together in a watch glass of hay infusion. Three clean 

 cover glasses were taken and on one was placed a drop of the 

 infusion from the watch glass with a few of the paramaecia, on 

 another was placed a drop with a few of the hypotrichs, and on 

 the third was placed simply a drop of the infusion. One of these 

 cover glass preparations was dropped into each of the three flasks 

 of culture medium already prepared, which were accordingly 

 designated P, H and respectively, signifying paramaecia 

 seeded, hypotrich seeded, and minus protozoa. The flasks were 

 then allowed to stand at room temperature for from five to ten 

 days, or until an enormous growth of the seeded forms had 

 appeared, and then the media were ready to be studied. These 

 three flasks thus contained the same culture medium and bacte- 

 rial flora, and one differed from the other only in the presence 

 of the protozoon with which it was seeded at the start. 



