466 MINNA E. JEWELL 



Measurements of regeneration were made by means of a caliper 

 and a metal metric ruler, obtained from Spencer Lens Company. 

 The tail was the only organ experimented upon. In making 

 averages there was no elimination of individuals, except in one 

 or two instances, and there note is made of the fact, and the 

 aberrant individual included in the table. 



APPARATUS AND METHODS 



Oxygen-free water was obtained from the water-boiling appa- 

 ratus in the vivarium at the University of Illinois, which has been 

 described by Shelf ord ('18). This apparatus consists primarily 

 of a boiler in which the water is boiled by means of high-pressure 

 steam until practically all of the gases are driven out, and from 

 which it passes into a tank covered by a hood where boiling is 

 continued until the water is freed of gases. The flow of water 

 into the boiler is regulated by a float-cock. The oxygen-free 

 water is withdrawn from the hooded tank, and passes through 

 cooling pipes in the room below where it is used. As it comes 

 from the pipes it contains no oxygen (Winkler method), and 

 is strongly alkaline, due to the CO2 having been expelled 

 by long boiling, and much of the bicarbonate having been 

 converted into carbonates. A series of different concentra- 

 tions of oxygen were obtained by siphoning the water through 

 a series of half-gallon mason jars (diagram 1), through alternate 

 ones of which air was bubbled. The water from the last of these 

 was siphoned into a 5-inch beaker, so that the level of the water 

 in the jars could not fall below 5 inches. It was found by titra- 

 tion that the oxygen concentration varied greatly in the different 

 parts of a jar through which a stream of air was passing, but was 

 relatively constant except at the surface in a jar through which 

 the water was being siphoned but no air was passing; consequently 

 the jars containing experimental animals were alternated with 

 those which were being aerated, with the result that each 

 experimental jar contained a little more oxygen than the one 

 preceding. 



