OBTAINING SIMULTANEOUS CULTURES 25 



apparatus, covered, and returned to the incubator for twenty- 

 four hours. The cultures first recorded as twelve hours will 

 then be thirty-six hours old, and so on. 



The apparatus appears to have a variety of other possible 

 uses, inasmuch as it is easy to set up relay make-and-break con- 

 nections, so that an incubator or a heating apparatus of any sort 

 may be turned on and off as many times as desirable up to 

 twenty-four hours instead of twelve, which is obviously a limit 

 of insufficient extent. It is felt that applications of this charac- 

 ter may be of a good deal of value in the study of conditions in- 

 volving time comparisons, and it is hoped that others may be 

 able to find the scheme of assistance in their work. The origi- 

 nal apparatus was constructed by the writer out of scrap materials 

 at a total expense, including the clock ($5.50) and exclusive of 

 time, of about $6. The improved apparatus was cast in alu- 

 minum and built up by the laboratory technical assistant at an 

 expense, exclusive of labor and inclusive of the clock, of about 

 $11. Details of model and construction will gladly be fur- 

 nished to those interested. 



