302 



Profs. Percy Frankland and Marshall Ward. 



of insertion of the septa, and, consequently, moments when elonga- 

 tion would be going on with least rapidity, because the cell-con- 

 tents were too busy with the act of division to be then growing at 

 quickest rates. 



Tn any case, it is obvious that the growth of even these young 

 filaments is a complicated phenomenon, and that the following points 

 at least have to be regarded in considering it. 



(1) There is the total elongation of the filament as a whole, and 

 (2) the growth of the individual segments or cells ; (3) the growth 

 of any one segment or cell is not necessarily going on at exactly the 

 same rate as a neighbouring one : this depends on the position and 

 on the age of the cell concerned ; (4) there is evidence to show that 

 the rate of growth of any cell or segment, and consequently that of 

 the filament, as a whole, is profoundly affected by several factors, 

 such as temperature, the nature of the food-medium, the presence of 

 other filaments which may aid the given one (at certain stages) by 

 increasing the peptonisation in the immediate neighbourhood though 

 we must believe that in other stages these neighbouring filaments 

 retard it by acting as competitors for the available food; and, lastly, 

 possibly light, some rays of which (perhaps blue) may retai d the 

 growth, while others (possibly the red and infra-red) may accele- 

 rate it. 



The following observations with the l/12th immersion were made 

 on segments of a two-days' growth in broth, with a trace of gelatine, 

 in bright light not direct sunlight at 17 to 18 C. 



A terminal segment showing three distinct septa, but already com- 

 posed of at least eight cells the other four (secondary) septa being 

 very difficult to observe was 54'6 /t long at 9.5 A.M. The growths 

 are shown in the following table, and, as before, we see that con- 

 siderable irregularity is observable in the rate from time to time : 



The segment was being pushed forward by the rest of the filament 

 at the rate of about 1 /* per minute 36'4 /t in 34 minutes actually 

 measured and was slightly undulating the whole time. In fact the 

 movement forwards, a scarcely perceptible series of jerks, reminded, 

 one of the movements of the hands of a watch. 



