288 Profs. Percy Frankland and Marshall Ward. 



in broth in which they were heated to 80 C. for two hours, and 

 somewhat more slowly in the same medium in which they were 

 boiled for a minute ; but after five minutes boiling they appeared to 

 be all killed, since none germinated out in six days at 20 C. 



Measurements of Growth of the Rods and Filaments. 



As will be evident from what has been said above concerning the 

 growth of the germinal filaments, they elongate in nearly a straight 

 line so long as they are free to do so and meet with no mechanical 

 obstruction. This fact, and the obviously rapid growth, led me 

 to a method for measuring the rate of elongation; and not only 

 did I succeed in doing this efficiently, but these growth measurements 

 carried me on much further and to some unexpected and interest- 

 ing results in another connection. 



On placing the eye-piece micrometer so that its vertical division 

 crossed the long axis of a filament shorter than the scale, it was easy 

 to observe the gradual extension of the filament as its ends passed 

 over the divisions. The value of each division was determined before- 

 hand, by examining a stage-micrometer with the same combination 

 as I used for the measurements. 



Having selected a nearly straight filament which extended over 

 twenty-seven of the fifty divisions on the scale, and having deter- 

 mined that each division was equal to 3 p for the power Zeiss 

 E occ. 2 employed, it was evident the filament was 81 /t long. 



It was growing in broth at 16 C. when put under observation at 

 10.10 A.M., and was watched for two hours, during which period the 

 thermometer rose from 18 C. to 20 C.* The microscope stood 

 under a shaded bell-jar at a south window, and the day was cloudy 

 and dull. 



At 10.22 A.M. i.e., twelve minutes after measuring the filament it 

 had elongated so as to cover thirty divisions instead of twenty-seven. 

 In other words it had grown 9 /* longer (fig. 13 a, 6) and had slightly 

 altered its slight curvature. At 10.45 it had grown another 12 n (fig. 

 13 c) ; at 11.30 it was longer by 18 ft, and at 12.10 its elongation 

 amounted to 24 /u. further. 



That is to say, in the interval from 10.10 A.M. to 12.10 P.M. (two 

 hours) the total growth in length of the filament amounted to 63 /t. 

 During the first twelve minutes the rate of growth was 0'75 ft, per 

 minute ; during the next twenty-three minutes the growth was at 

 the rate of nearly 0'5 /t per minute ; during the next forty-five minutes 

 it was at the rate of 0'4 ft per minute ; and during the last forty 

 minutes at the rate of a little over 0'5 fi per minute. 



These facts may be conveniently tabulated as follows : 

 * Air temperatures throughout, except where specially given as otherwise. 



