432 Profs. Percy Frankland and Marshall Ward. 



13 14 15 16 17 18 19 Z\ E2 E5 24 85 Ib 17 Z8 29 SO 31 



59 34 



On examining these three curves, AB, CD, and EF,* we see that 



1. The general tendency of the weak gelatine i.e., poor in food 

 materials but stiff in consistency (Curve AB) is to lengthen the 

 doubling period. 



2. That considerable irregularities occur at all the temperatures 

 higher than about 24 C. or 25 C. These are no doubt due to the 

 inequalities in the phase of growth, different ages of the culture, and 

 so on, already discussed. 



3. It looks as if the curve suddenly shot up at t emperatures beyond 

 3132 C., as shown by the curve for broth (CD ). 



4. It might, perhaps, be suggested that although the addition of 

 gelatine delays the doubling period, it also delays the attainment of 

 the maximum temperature, i.e., it protects the food-drop against 

 exhaustion, until a higher temperature than that at which exhaustion 

 sets in when broth alone is used. This may be the case, but I do 

 not regard it as proved, and there are many difficulties with broth- 

 cultures at higher temperatures, as already said . 



But (5) it is clear that these three curves, unsatisfactory though 

 they are as yet in detail, show striking general resemblances to a 

 curve of respiratory activity the steady fall in the doubling period 

 as we pass from lower temperatures, and the sudden rise again beyond 

 31 C. (seen in the broth curve) being very suggestive and I believe 

 that is what they really are, for reasons already discussed. 



Having so far cleared the way for the understanding of these 

 curves, we shall see that when attention is carefully given to all the 

 points discussed, a much more regular curve is obtained, as the 

 following series show. 



* Curve AB summarises the averages for weak gelatine ; CD, those for broth 

 + 1 per cent, gelatine ; EP, those for broth alone. The ordinates are minutes and 

 the abscissae temperatures. 



