Viability of U red inio spores 
o 
tures below 25° C., a highly satisfactory method was devised. 
Mr. Robert W. Goss, my associate, shares equally in the gradual 
development of this method of maintaining low temperatures. In 
developing this method, we went on the principle that it is much 
easier to maintain constant temperatures in incubators above the 
temperature of the surrounding medium than it is to maintain 
temperatures lower than that of the room in which the incuba- 
tors are kept. 
Four two-door ice boxes (14 by 22 by 36 inches, inside 
measurement) were obtained, the ice compartments dismantled, 
and two extra shelves put in each box so that the working ca- 
pacity of the boxes was doubled (fig. 1). 
These boxes were equipped with heaters which were made as 
follows: Chromel wire was wound on two strips of transit and 
fastened to the underside of a large (12 by 19 in.) transit plate 
having a row of holes in the center the length of the plate. The 
whole was then set up from the floor of the boxes (2% in.) by 
means of porcelain insulators. 
The chromel wire was connected up in parallel. The warm 
air came up thru the holes in the transit plate and also along the 
walls of the boxes. In this way a very uniform temperature was 
maintained thruout the box so that there were no measurable 
differences between the temperatures on the upper and lower 
shelves. 
For constant temperature controls, the thermostats made by 
the Chicago Surgical and Electric Company were employed. These 
were fastened in the center of the back wall of the boxes. The 
necessary electric connections and pilot lamps completed the 
equipment (fig. 2). 
The incubators were then installed in a cold storage room 
which was maintained at a more or less constant temperature of 
4° C. or slightly below. The thermostats in the incubators were 
so set that temperatures of 5°, 10°, 15°, and 20° C. were main- 
tained in the respective incubators. In no instance did the tem- 
perature in any one of the incubators vary more than one degree 
either way during the course of the experiment. 
Readings were made three times a day and very little regula- 
tion of the thermostats was required, altho it was necessary to 
adjust and file the contact points occasionally. 
During one year’s experiments, even tho all the incu- 
bators were maintained at temperatures above that of the cold 
storage room, we could notice no effect on the constancy of the 
