DIVISION RATE IN CILIATE PROTOZOA. 305 



with theirs, the question for mammahan thyroid, at least, seems 

 fairly well settled. 



Nowikoff 's work suggested to us the query whether or not his 

 results could be taken as widely significant.^ Our purpose has 

 been, therefore, to add to the known facts along this line by 

 ascertaining the influence of glands taken from each of the five 

 main subdivisions of vertebrated animals, so far as they or sub- 

 stances derived from them, affect certain protozoa; and, using 

 division-rate as an index, to thus get a line on the comparative 

 physiology of this gland. 



Materials and Methods. 



Perfectly fresh thyroid glands were taken from the fresh-water 

 sucker {Catostomus teres), the frog {Rana pipiens), the turtle 

 (Cistudo Carolina), the chick {Gallus domesticus) , and the cat 

 (Felis domestica) , dissected as cleanly as possible from surround- 

 ing tissues, and then dried by moderate heat; each was then 

 ground to powder in a mortar, and the material then kept in 

 vials till used. In the instance of the mammalian gland, fatty 

 tissue was present in such amount that this was dissolved away 

 by repeated washing in ether to bring the gland to such condition 

 that it could be finely pulverized. In supplying thyroid material 

 to protozoa in this form, we endeavored to avoid any alteration 

 in its character such as might result in the making of glycerin or 

 alcoholic extracts. This seems a point which should be rather 

 carefully guarded. 



The forms employed for experimentation were Stylonichia and 

 Param(scium. To familiarize ourselves with a method of hand- 

 ling such organisms, and also for the purpose of securing indi- 

 viduals whose ancestry would be known to us, we first carried 

 isolated "wild" forms through a considerable number of genera- 

 tions (in the case of Stylonichia, seventy-four) ; we employed 

 depression slides, kept in a moist chamber, each slide carrying 

 four drops of bacterial hay infusion made up in the manner of 

 that used by Woodruff ('05) in much of his work. The "wild" 

 specimens were taken from ordinary laboratory cultures, but the 

 particular individuals used in any given experiment were taken 

 from the pedigreed lines descended from a single parent. The 



1 Our work was completed before Shumway's article appeared. 



