EFFECTS OF THYROID ON PARAMAECIUM 



547 



The line which had been drawn from the control only fifteen 

 days before and treated with boiled thyroid continued at a high 

 rate of division while the control and thyroid lines cited above 

 were undergoing their last depression period. From this an- 

 other line B" was drawn and returned to the control medium. 

 Table 18 gives the division rate of these two lines for the fol- 

 lowing one hundred and twenty-five days, during which the line 

 treated with boiled thyroid di\dded at a rate of 0.70 of a di- 

 vision per day more rapidty than the line derived from it and 

 subsequently maintained in hay infusion. And in figure 5 are 

 shown graphically the life histories of these two lines, where 

 again the close similarity of the two curves may be observed. 



TABLE 19 



Race B. Summary of experiments. Average division rate -per day 



Percentage increase produced by thyroid feeding, 64 per cent. 



Finally in table 19 is given a summary of the average daily 

 di\dsion rate of the control and thyroid lines respectively ob- 

 tained in all the experiments performed with race B, A com- 

 parison with table 10 shows that the effect of the thyroid is not 

 at first sight so marked in the caudatum race (an increase of 

 0.55 division per day) as in the aurelia race (an increase of 1.05 

 divisions per day). This difference disappears when we com- 

 pare the average division rates of the control lines for the two 

 species (0.85 and 1.60 divisions per day respectively) and we find 

 that the percentage of increase in the two races is practically iden- 

 tical, being 65 per cent for Race A and 6Jf. per cent for Race B. 



c. On the C race. The third race of Paramaecia, C, was es- 

 tabhshed in order to observe in greater detail the other effects 



