310 Profs. Percy Fraiildand and Marshall Ward. 



The doubling periods* calculated on the curves were as follows : 



1. Dark culture. 



Approximate 

 (air) temps. 



15 30 fi = 2.30 to 3 P.M. = 30 minutes at 23'0 21-75 C. 

 30 60 = 3.0 3.40 = 40 21-7521 

 60-120 = 3.40 4.37 = 57 21 20'5 

 120240 = 4.37 5.40 = 63 20'5 20 

 240480 = 5-40 7.4 = 104 20 -19 



Now my constant temperature cultures in broth in the dark at 

 232175 run from 32 minutes at 2324 C. to 63 (at 2021) and 

 at 18 19 C. the extremes are 67 78 minutes ; the range is a wide 

 one i.e., 32 78 but it may be regarded as including the above 

 cases, or very nearly so, and perhaps, therefore, the air- temperatures 

 given did not depart far from those of the culture cells. 



2. The culture in the light for the same date has the following 

 doubling periods : 



Approximate 

 (air) temps. 



25 50 fL 2.324.12 100 minutes at 23 21 C. 

 50100 = 4.125.53 = 101 21 19'5 

 100200 = 5.537.20 = 97 19-518 



And there is nothing comparable as regards time with such long 

 periods anywhere in my broth cultures at constant temperatures, in 

 the dark. 



Unless, therefore, we assume that the air- temperatures given depart 

 very widely, in different ways, from the real temperatures of the cul- 

 ture-drops, we must assume that the lower growth in the exposed 

 culture was due to inhibition by the light rays. 



Probably the most startling fact which comes out on examining 

 these results is the extremely rapid growth of the dark culture from 

 6.41 onwards. To explain this it is necessary to point out one or two 

 things not obvious at all. In the first place, as the filament grows 

 longer there are more and more cells formed by the repeated bi-par- 

 tition i.e., there are more and more elongated segments in the chain, 

 and therefore a greater elongation of the whole as the sum of the 

 growths of the individual cells becomes greater. Then, secondly, the 

 vigour of the entire cell-series evidently increases as the feeding and 

 other powers e.g., peptonising activity, &c. increase. 



Consequently, after a certain period these strongly developing fila- 

 ments which have not been exposed to any disturbing agent, grow at 



* The doubling period is the time required for a given length, of filament to 

 double this length (see p. 403). 



