66 



RELATIONSHIPS OF THE COCCACE^E 



the labor involved, and we have limited our observations 

 on optimum temperature to the comparison of growth 

 and color production at 20 and 37 degrees. Cultures 

 were grown for this purpose on agar for two weeks and 

 compared by inspection. Amount of growth and depth 

 of color were recorded in five arbitrary grades accord- 

 ing as growth or color production was much better at 

 20 degrees, somewhat better at 20 degrees, equal at the 

 two temperatures, somewhat better at 37 degrees, or 

 much better at 37 degrees. 



Thermal death-points were included in the original plan 

 of our experiments and observations were made on 87 cul- 

 tures. The process used was to inoculate, from 3- to 5-day- 

 old agar cultures, into broth tubes brought to the desired 

 temperature in a water bath heated electrically by a 

 platinum coil, and to expose them for ten minutes. The 

 tubes were then cooled and incubated at 37 degrees for 

 six days. At the end of that time, streaks were inocu- 

 lated from the broth tubes in order to make sure by 

 characteristic growth that the organisms originally 

 inoculated were present. Tests were made from 50 

 degrees up to the point where growth failed. The 

 general results obtained are as follows: 



THERMAL DEATH-POINTS. 87 CULTURES OF COCCI. 

 Number of Cultures Killed at Various Temperatures. 



