1Q12] Lorande Loss Woodruff 411 



mentioned point to the conclusion that paramaecia excrete sub- 

 stances which are toxic to themselves and that these substances, as 

 one would expect, are more effective when the organisms are con- 

 fined in limited volumes of culture medium. 



The logical method of procedure was to determine the influence 

 of media known to be contaminated with the excretion products of 

 large numbers of paramaecia. A series of experiments were accord- 

 ingly made with media which, it is beHeved, were identical except 

 that one contained the products of metaboHsm of a heavy growth 

 of paramsecia, while the other was absolutely free from such con- 

 tamination. The lines of organisms subjected to the medium which 

 had previously been the abode of numerous paramaecia reproduced 

 much more slowly than those in the uncontaminated medium, so 

 it is obvious that culture media in which paramaecia have been 

 living have a decidedly depressing effect on the rate of reproduction 

 of ParamcEcium. All the results indicate that the excretion products 

 of Protozoa play an appreciable part in determining the period of 

 maximum numbers, rate of decline, etc., of the fauna of hay 

 infusions.^^ 



SUMMARY 



The chief points which, I believe, the studies on the physiology 

 of this race of Paramccciiim have shown are : 



1. The protoplasm of a single cell has the potentiality to repro- 

 duce by division indefinitely — under iavorable environmental con- 

 ditions — and therefore conjugation, or fertilization, is not a neces- 

 sary phenomenon for the continued life of protoplasm. 



2. The more or less general opinion that a constant environ- 

 ment is detrimental to breeding stock and results in decreased 

 activity, degeneration and sometimes death, is not substantiated by 

 the results from this culture on a constant environment of beef 

 extract. The fact that these experiments were on the protoplasm 

 of one of the simplest animals, indicates, I believe, that the prevail- 

 ing opinion is based on observations which include incidental com- 

 plicating factors not recognized. 



"Woodruff: Observations on the origin and sequence of the protozoan 

 fauna of hay infusions. Journ. Exper. Zoology, vol. 12, no. 2, 1912. Fine: 

 Chemical properties of hay infusions, with special reference to the titratable 

 acidity and its relation to the protozoan sequence. Ibid. 



