GROWTH OF MASSIVE CULTURES OF BACTERIA 33 



may be easily moved about the room. An inner tank, two 

 inches shorter and two inches narrower, also provided with 

 a trough that runs around the edge, sits in the large one, 

 and is supported two inches from the bottom of the larger 

 one by iron cross-bars. The bottom of the outer tank and 

 the seal trough on its edges are filled with water. The seal 

 trough of the inner tank is filled with glycerin. Both lids 

 are raised and lowered by wire ropes passed through pulleys 

 fixed in the ceiling. The iron frame supporting the tanks 

 may be of any desired height. In our incubating room we 

 have a nest of six tanks, three of which are on frames four 

 feet high and three on frames two feet high. This economizes 

 space, as the lower ones can be rolled under the higher ones. 

 Both lids are supplied with vent tubes which are plugged 

 with cotton in sterilization. Twenty liters of 3 per cent, 

 agar is placed in the inner tank; both lids are lowered into 

 their respective troughs, and with large gas burners at full 

 blast underneath the apparatus is a sterilizer. After three 

 sterilizations on successive days the medium is inoculated 

 by pouring a liquid culture through the vent tubes in the 

 lid of the inner tank. Then with upper lid lowered into 

 the water trough and gentle heat, which may be controlled 

 by a thermoregulator, it becomes an incubator. With a 

 number of tanks in a small room it is better to heat the room 

 to the desired temperature, thus regulating the heat, than 

 it is to heat each tank separately. 



When the growth has reached its maximum, the time 

 necessary for this varying with the organism grown and the 

 temperature maintained, both lids are raised, the growth 

 is detached from the subjacent agar with sterilized bent 

 glass rods, sterile salt solution added if necessary, and the 

 bacterial mass is drawn by means of a water pump into a 

 sterilized receiver. 



The tanks are inoculated from special glass bulbs in which 

 the organism has been grown for some days. With the 

 colon bacillus we have usually employed Uschinsky's 

 solution, or some modification of it, in the inoculating bulbs, 

 in order that there may be no trace of foreign protein in 

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