550 WALDO SHUMWAY 



Experiments with boiled thyroid (tables 16, 17, and 18) have 

 demonstrated that it produces effects similar to those of the raw 

 and desiccated gland substance. The agent at work is not ex- 

 tracted by boiling as shown by parallel experiments with the 

 filtered bouillon. It may be noted in this connection that Oliver 

 and Schafer ('95) reported that boiled thyroid produced the same 

 depressant effect on heart action as the untreated gland. If the 

 results obtained in these experiments are due to a hormone 

 secreted by the thyroid it must be one of remarkable stability. 



Attention is called to the constancy with which the effect of 

 the thyroid has been observable during extended periods of daily 

 treatment (figs. 4, 5, and 6). In the longest individual experi- 

 ment (one hundred and forty days) the thyroid fed line divided 

 more rapidly than the control in every period. Nor has this 

 rapid rate of division produced any harmful effects. In no case 

 has a thyroid fed line died out before its control. 



At many different periods lines have been instituted from 

 thyroid lines of long standing and abnormally high division rates, 

 returned to the control medium and continued as parallel lines to 

 the parent thyroid and control lines (Experiments A 1, A 5, 

 B 6). In every case the thyroid-control line slowly returned to 

 the normal (hay infusion) rate of division. No unusual rise in 

 the death-rate marked the transfer. It may be remarked in 

 this connection that the transfer from hay infusion to thyroid 

 media is also unaccompanied by any unusual mortality. 



It is of particular interest to observe the effects of the thyroid 

 at times in the life history when the race is undergoing a depres- 

 sion period. It has been shown by Calkins ('04) that a number 

 of different factors may be involved in carrying a line through 

 this critical period. He has demonstrated that the mechanical 

 agitation of a railroad journey, a sudden change of diet, a dif- 

 ference in the salt content, or an increase in temperature may 

 be sufficient to restore a weakened line to its normal vitality. 

 According to his interpretation this power of inducing regenera- 

 tion is the essential feature of conjugation. The recent sugges- 

 tive observations of Woodruff andErdmann ('14) show that the 



