GROWING BACTERIOLOGICALLY STERILE POTATO PLANTS 5 
was supplied on the inside with one half of a brass pipe union. The 
arrangement of the attachments to the kettle appearing above the 
floor line is shown in Plate 1 . 
THE BOILER 
Steam was generated in a vertical steam boiler of a size rated at 5 
horsepower. The boiler had all the customary attachments of pet 
cocks, gauge, injector, and a safety valve set to release at 100 pounds 
pressure. The steam was carried directly to the kettle through a 1- 
inch steam line controlled with a single gate valve. This boiler is 
shown in Plate 1 behind the kettle. 
TRANSPORTATION OF CANS 
After filling and before planting the cans were moved many times. 
For convenience in handling them two pieces of 1-inch pipe 5 feet 
long with hooks in the middle were used. The hooks were caught 
in the bail eyes and the can lifted and carried by two men. The 
hooks were made by welding a ring around the middle of the pipe, 
the ends being drawn out and bent into hook form. The method of 
drilling the pipe and passing the straight shank of a hook through it 
failed, as the holes so weakened the pipes that they bent easily. 
At the kettle a half-ton chain block suspended from a movable 
trolley rolling on an I beam overhead was used. The cans weighed 
about 260 pounds (118 kilograms) and had to be raised at least 3 feet 
above the floor and lowered 6 feet into the kettle. Any point in the 
kettle and for 6 feet in front of it was accessible to the block and 
trolley. The cans were suspended from the hook of the block by an 
evener. The evener was made of a crucible-steel tube 16 inches long, 
with strong, short drop chains and hooks at the ends to attach to the 
bail eyes, and a ring at the center to suspend it from the block. 
The chain block, trolley, and a portion of the I beam appear in 
Plate 1. 
ELECTRICAL-RESISTANCE THERMOMETER 
For the purpose of ascertaining the temperature in the interior of 
the cans and kettle an electrical- resistance thermometer was used. 
The three wires from the resistance bulb were encased in a lead cable, 
which terminated in the complementary portion of the pipe union, the 
other part of which was attached to the rim of the kettle. The resist- 
ance bulb was planted in the center of a can, the soil properly packed 
around it, the free ends of the wires passed through the hole in the 
rim, and the union connected. The wires were properly attached to 
the indicator outside. These are shown at the left of the kettle in 
Plate 1. 
ASEPTIC CULTURE HOUSE 
When a sterilized can was opened for any purpose this had to be 
done under aseptic conditions. As the cans were difficult to handle 
and as they usually remained open for 20 to 30 minutes at a time, a 
special culture house was provided in which they could be manipu- 
lated. 
This house consisted of a practically air-tight box, 6 feet in each 
dimension, and well painted inside and out. A narrow doorway at 
the front, closed with a sliding door, was the only opening. The 
