446 Profs. Percy Frankland and Marshall Ward. 



Further examination of this culture brought out very clearly the 

 difficulties of these high temperatures. I started measurements at 

 6.28, 7.58, and 8.23 P.M. respectively, but each had to be abandoned 

 after less than a quarter of an hour, owing to the excessive dilution, 

 due to the powerful absorption of water by the (melted) gelatine 

 drop, which induced currents and floated the rodlets away. 



The general result was that the longer the culture remained at the 

 high temperature the slower the growth. No doubt the dilution was 

 largely responsible for this, but another cause may have been the 

 slowing action of the high temperatures, taking time to act on the 

 filaments. 



It is by no means improbable, comparing all one has observed of 

 these cultures at high temperatures, that the bacterium goes through 

 a grand period of growth, i.e., it begins growing slowly, attains a 

 maximum, and then slows down again until fully outgrown. This 

 being so, the total length of bacterium obtained (which, in other 

 words, represents its total crop, or dry weight) will depend on the 

 following factors : 



1. The amount of available food material. This I cannot measure, 

 because it is not necessarily the amount of broth, or gelatine, &c., but 

 the amount of peptonised materials, &c., it can get from the medium. 



2. The temperature. At the optimum it metabolises, and grows, 

 and respires, &c., at its best ; but at higher temperatures removed 

 from that it may grow for a short time more rapidly, but sooner 

 exhausts itself, and so produces a poorer crop in the end. This cer- 

 tainly seems to be the case with these high temperature cultures, 

 for I never get anything like so large a crop at 30 35 C. as at 

 22 25 C., other things being equal. Moreover, it seems clear that 

 though the growth may for a short time be as rapid as it is near the 

 optimum, it soon slows down (e.g., compare Novembers experiments). 

 All this suggests that at temperatures above the optimum, the 

 machinery of the cell is being worked at too high a speed, and comes 

 to grief sooner or later. How far this is due simply to over-respi- 

 ration and rapid exhaustion of the oxygen in the medium, or to 

 inability to peptonise or digest the food-materials, or other causes, it 

 is impossible to say with certainty. Probably the matter is extremely 

 complex, however. 



3. The amount of water in the medium. I have repeatedly 

 pointed out my suspicion that variations in the growth result from 

 variations in the precipitation or absorption of water in the culture- 

 cells. It is not easy to trace the effects to mere dilution of the 

 food materials, however, and it is quite possible that in all cases 

 slight, but perceptible, changes of temperature accompany these 

 evaporations and precipitations, &o. In some cases, at any rate, the 

 dilution is traced to precipitations due to slight draughts, causing 



