268 THE PLANT WOKI>D. 



rert sugar, but in some manner the sugar and the enzyme fail 

 to reach each other ; that is. the enzyme is localized. This is 

 notably true with the Saffraia variety, which, when ripe, I'etains 

 a relatively small but permanently residual amount of oane 

 sugar. 



Arizonn Agricultural Experiment Station, 

 Tucson, Arizona. 



AN ELECTKIC THEEMOEEGULATOK FOE PAEAF- 

 FINE BATHS AND INCUBATOES. 



By Dk. W. a. Cannon. 



The electric thermoregulator to be described here has been 

 in use for several months and has proved so satisfactory that 

 an account of it at this time seems warranted. It may safely 

 be employed for controlling the electric heating device for tem- 

 peratures ordinarily employed in the laboratory. With the 

 stove and oven used in this instance the amplitude of the range 

 of temperature does not surpass two or three degrees Centigrade, 

 and the regulator itself is sensitive to one-tenth of a deo;ree or 

 less. 



The entire heating and controlling device consists of the 

 primary or lighting circuit with the stove, and the secondary 

 circuit with the automatic switch and regulator. The stove is 

 of the ordinary type, with a flat upper surface upon which 

 the oven stands. A sine-le cell of the Edison Primarv batterv 



O It 



proved very satisfactory for generating the secondary current. 

 As in the case of the stove and battery, so in that of the auto- 

 matic switch, any good type may be employed. The switch 

 used, however, is a stock automatic one which is remodeled so 

 that it is operated by a tw^o-way in place of a three-way seci:)n- 

 dary circuit, and is peculiar in having stationary poles made of 

 copper combs with four teeth in place of the troublesome car- 

 bon or expensive platinum usually used. A copper wedge, in- 

 sulated from the arm that bears it, is pulled by the magnet in 

 the secondary circuit into the space between the poles, and thus 



