394 Profjg. Percy Frankland and Marshall Ward. 



generally, on the growth of bacteria, so far as their macroscopic 

 characters are concerned, and a few observers notably Brefeld with 

 B. subtilis have made observations on the rate of cell-division at one 

 or two principal air-temperatures ; but, so far as I know, no one has 

 attempted to measure quantitatively and in detail the effect of small 

 differences of temperature over a long range, and that temperature 

 that of the culture which we have seen may be different from that of 

 the air and especially to obtain plotted out curves of growth under 

 such conditions. 



It is obvious that my methods admit of this being done, and I 

 thought it might be not only productive of -useful information as to 

 the primary point concerned the definite effect of given tempera- 

 tures on the growth but that I might possibly be able to make use 

 of these normal temperature-curves indirectly, by comparing them 

 with the foregoing. 



I accordingly started what proved to be a very long and laborious 

 series of cultures under a microscope enclosed in an incubator of an 

 improved form modelled on the original type described some years 

 ago by Sachs. The chief difference is that the heating arrangement 

 is a thick, flanged, blackened, iron plate, on which stands a thick 

 sheet of asbestos-board, and on this the microscope. The whole body 

 of the microscope, except the eye-piece and micrometer screw, is 

 enclosed in a wooden box, of which the iron plate is the floor ; this 

 box has a glass window in front and two lateral openings (with 

 shutters) for manipulating the culture, and can easily be opened 

 entirely if necessary. 



A culture being placed in position, and the microscope focussed on 

 a selected rodlet or filament, the shutters are all closed and the 

 growth goes on in the dark. 



The temperature is registered by a thermometer whose bulb is 

 inside and reading column projecting through the roof : the gas 

 passes through a very delicate thermo-regulator, containing mercury 

 and ether, and when once the apparatus (which I shall henceforth 

 term Sachs' box) is heated up, it can easily be kept at a temperature 

 so constant that it does not alter a degree in several hours, while, 

 with a little more care (and provided no large alterations of tempera- 

 ture are going on in the room), it will remain for hours within 

 0'25 C. of the temperature arranged for. 



Of course, the temperature falls or rises quickly when the box is 

 opened unless it is that of the room but it returns in five to ten 

 minutes if the opening and shutting are completed in a minute or so ; 

 the opening and shutting of the side windows, and the removal and 

 replacement of the shutter during observations, produce very slight 

 slowly acting effects, which, however, cannot be neglected, as we 

 shall see. 



