5^9 
• Balls . Temperature and Growth. 
The growth-curves plotted from the results of these experiments show 
a steady acceleration of growth with rise of temperature, which corresponds 
fairly well to the expectation based on Van ’t Hoff’s law until 30° C. is 
reached. Above 30° C. this acceleration decreases, and the curve begins to 
flatten as the ‘ time factor * comes into noticeable operation. At a fairly 
definite temperature growth ceases and the curve becomes horizontal. The 
temperature at which this cessation of growth takes place is commonly 
called the ‘ maximum but in view of the results obtained in this research 
it seems advisable to drop the word for the present ; I shall refer to this 
point in the growth-temperature curve by the provisional title of ‘ stopping- 
point ’. 
The form of the upper part of the curve as it falls off to the horizontal 
is very variable ; even at the same rate of heating it is not neccessarily the 
same, and it is flatter when the cultures are heated more slowly than the 
usual rapid rate employed. In a few cases the curve almost coincided with 
the theoretical expectation, the falling off of the growth-rate being scarcely 
noticeable until a minute before complete cessation. It will appear subse- 
quently that these variations are probably due to differences in the freedom 
of osmosis from cell to medium, of the poisonous excreta. 
The ‘ optimum ’ thus appears as the temperature at which the time 
factor and the temperature acceleration are in equilibrium, and it is not in 
any way a definite point. The word will not be used again in this 
connexion. 
More interest centres round the stopping-point. When all allowances 
have been made for errors of observation, it is certain that with the present 
apparatus the point can be determined to within 0-3° C. of accuracy, or even 
less. The differences actually recorded are much more than this observa- 
tional error ; the stopping-points lie between 37 0 C. and 38-3° C., with one 
exception which will be described shortly. These variations will be seen at 
a later stage of the paper to be in all probability due to varying freedom of 
osmosis, provided that the rate of heating is approximately the same in each 
experiment. 
The exceptional case, which in itself supports this idea, was the first 
reading of a double observation. The hypha almost stopped at 37-5° C., 
bent slightly at the tip, and continued to grow slowly until 40-5° C. was 
reached. The new portion bore the appearance of having burst out from 
the end of the hypha through a weak, though unbroken area in the cell- 
wall ; this mark enabled the slight growth to be determined with absolute 
certainty. The second determination on this hypha after cooling down 
gave a reading of 37-4° C. The fact has some importance, for it shows that 
the cessation of growth is not due to any inability of the protoplasm to 
perform constructive metabolism beyond 38° C. 
The principal point to notice, in view of subsequent results, is that in 
no case was the stopping-point depressed below 37-0° C. 
