308 



WALDO SHUMWAY 



Another source of error in these experiments Hes in the ab- 

 sence of an attempt to secure closely related Paramaecia for the 

 experiment, the necessity for which is shown by the great varia- 

 bility in reaction and viability possessed by different races and 

 individuals of this form. 



I have endeavored to calculate from Nowikoff 's daily counts of 

 individuals the number of divisions which took place, although 

 as I have pointed out this is made difficult by our ignorance 

 of the number of deaths which occurred. This calculation is 

 shown below, and indicates that using the rate of division 

 as an index, his results are inconclusive. 



Calculated division rate for Nowikoff's Paramaecia treated ivith Thyroid, Hay 



Trifusion, and Muscle 



Hay Infusion. 



Thyroid 



Thyroid 



Muscle 



Hay Infusion . 



Thyroid 



Thyroid 



Gudernatsch, in his second study of feeding experiments on 

 tadpoles ('13), describes an experiment in which small pieces of 

 thyroid gland were placed "in a small glass vial closed with gauze 

 and allowed to stand upright, the open end being under the sur- 

 face of the water." The typical rapid macroscopic differen- 

 tiation normally produced by thyroid feeding was observed, and 

 Gudernatsch concludes that "the product of the thyroid which 

 caused the rapid differentiation must be soluble in water." The 

 conditions of the experiment do not however preclude the possi- 

 bility of minute particles of the thyroid escaping through the 

 gauze and becoming fooc^for the tadpoles. A definite conclusion 

 can only be drawn from experiments conducted with carefully 

 filtered preparations. 



