304 WALDO SHUMWAY 



one days thyroid treatment individuals were taken from the X 

 line, returned to the control medium to initiate the Y line. 

 The table shows the great increase produced by the thyroid in 

 the D line and the subsequent return to normal in the Y line. 

 The Z line derived from the Y line and treated with thymus, 

 shows nothing significant. 



Experiment VI. August 12 to 21, 1913. 



Average Division Rate 



A a 



'^^'°'* (control) (thtroid) 



32 1.70 1.85 



33 2.25 3.70 



As the control line began to emerge from the depression period, 

 another race (a) was derived from it and treated with Thyroid Y 

 as above. After one period in which no significant increase ap- 

 peared, the thyroid treated line presented a high division rate, 

 comparable with that shown in Experiment V. 



Experiment VII. August 22 to September 5, 1913. 

 Average Division Rate 



34 

 35 

 36 



A 

 (control) 



a' d' 



(thyroid) (thymus) 



2.50 3.10 2.50 



2.30 3.25 2.00 



2.40 3.25 2.95 



This experiment is rendered more significant by the fact that 

 instead of four files, eight files were maintained for each line. 

 The table shows the significant increase in division rate exhibited 

 by the thyroid treated line. Note also that in this as in other 

 experiments where Thymus V was employed, that the dried 

 thymus does not produce the decrease in division rate observed 

 when the fresh glands were used. It may be said in passing that 

 this decrease was due to the large number of deaths which ap- 

 peared in those lines. 



