EFFECT OF THYROID ON DIVISION OF- PAR.^MAECIUM 303 



the division rate as a rule averaged much higher than it had in the 

 city. As my supply of Thymus and Thyroid IV was limited, and 

 owing to the difficulty of keeping fresh tissue, this experiment 

 was continued for one period only. It is sufficient however to 

 show the typical thyroid increase. Compare the following ex- 

 periment. 



Experiment IV. June 28 to July 7, 1913. 



Average Division Rate 



This experiment was carried on at the same time as Experiment 

 III. The control in this case was the D line (now known as D') 

 which had been treated with thyroid for 9 periods and then 

 maintained on a control medium since the close of Experiment I. 

 While in this medium it had approximately given the same 

 averages as A, as may be seen from diagram 2. The O line was 

 derived from this and treated with Thyroid IV for two periods, 

 during which, as may be seen from the table, it maintained a 

 much higher rate of division. 



Experiment V. August 7 to 21, 1913. 



Average Division Rate 



At the time of this experiment the life-cycle shows an apparent 

 depression period (diagram 2) and the race was reduced to two 

 individuals. One of these was kept in the control medium to 

 continue the A line, the other was treated with Armour's desic- 

 cated sheep thyroids (Thyroid V) to start the X line. After 



