212 STUDY OF THE PHYSIOLOGY OF BACTERIA 



has constructed a device which answers every purpose for a 

 small class. The diagram, Fig. 140, explains it. 



The thermal death-point is determined by exposing the 

 organisms in thin tubes of broth at varying temperatures 

 for ten-minute periods and then plating out to determine 



b' 



^ 



Fig. 140. — Diagram of fittings for a cold incubator. 1, small tank for 

 constant head, about one foot in each dimension: a, inflow; b, overflow; 

 c, lead pipe. 2, refrigerator: a, ice; b', fiat coil under ice; c', outflow 

 to incubator. 3, incubator: a", cold water inflow; b", overflow; ther- 

 mometer and burner omitted. The diagram explains the construction. The 

 water cooled to about 14° with artificial ice by flowing through the lead coil 

 under the ice flows into the incubator, which may be heated and regulated 

 in the usual way. 



growth. The effect of heat may also be determined by 

 exposing at a given temperature, e. g., 60° for varying 

 lengths of time and plating out. 



B. Oxygen relations— whether the organism is aerobic, 

 anaerobic or facultative is determined by inoculation in 



