EFFECT OF THYROID ON DIVISION OF PARAMAECIUM 307 



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Diagram 3 Chart showing comparative effects by five day periods of Thj'- 

 roid II and Thyroid III. The ordinates represent the increase of the thyroid 

 average over the control average per period, the abscissae the periods covered - 



= Thyroid II = Thyroid III 



distilled water, shaken and filtered two or three times through 

 paper, in a one or two per cent solution. A number of individuals 

 (one to three) were placed in a few drops of this extract on a 

 slide; other indis^iduals were placed in a similar quantity of hay 

 infusion or^ther media. The preparations were covered with a 

 cover slip and set aside in a moist chamber. Daily observations 

 were made and showed larger numbers of individuals in the 

 thyroid media than in the others. 



This method of Nowikoff' s does not seem, however, adapted 

 to answer the question at issue. Woodruffs experiments ('11) 

 upon the toxicity of the material excreted by Paramaecia have 

 shown that the division rate of individuals kept in the same 

 medium for a number of days grows slower owing to the harm- 

 ful effects of this excreted material. It is significant that in 

 Xowikoff's experiments the Paramaecia kept in hay infusion 

 under these conditions died out in a few days, as we should 

 expect. Then too the thyroid extract, kept in a moist and fairly 

 warm chamber for periods up to a month, must have undergone 

 appreciable chemical change. It is evident that the experiment 

 is complicated by the introduction of a toxic, if not lethal, 

 factor and by the lack of a uniform thyroid preparation. 



