THE EFFECT OF EXCRETION PRODUCTS OF 



PARAMAECIUM ON ITS RATE OF 



REPRODUCTION 



LORANDE LOSS WOODRUFF 

 Sheffield Biological Laboratory, Yale University 



ELEVEN FIGURES 



Evidence from many sources points to the fact that a consider- 

 able amount of the products of metaboHsm of a cell is frequently 

 injurious to the cell. As is well known, alcohol in excess of a 

 certain amount inhibits the reproduction of yeast, while the 

 same amount forms a favorable medium for the organism which 

 produces vinegar. Again, vinegar in excess of a certain quantity 

 is toxic to the cells -^hich are responsible for its formation, but 

 serves in turn as a favorable environment for organisms which 

 give rise to another type of fermentation. 



De CandoUe^ nearly eighty years ago apparently suggested 

 that low crop production, following continued growth of one crop 

 in the same soil, is due tckhe accumulation in th^iutrient medium 

 of deleterious organic substances originating in the growing plants 

 themselves. Liebig^ also held this view for a time but later aban- 

 doned it in favor of the idea that the beneficial effect of crop 

 rotation is due to the several crops requiring different substances 

 or varying proportions of the same substances, and that the dis- 

 turbance of the balance in the soil produced by one crop is not 

 unfavorable to the growth of some other crop. The trend of 

 much recent research is distinctly in support of the view that 

 substances are produced by the higher plants which are speci- 



1 DeCandolle, Physiologie vegetale, Paris, 1832. 



2 Liebig, Complete works on chemistry, Familiar letters on chemistry, letter 12, 

 p. 35, 1852. Cf. Gilbert, Bull. 22, Office Exp. Sta., U. S. Dept. Agr., 1895. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 10, NO. 4 



557 



