650 Proceedings of the Royal Society of Edinburgh. [Sess. 
It is the object of this paper to show that this simple law is in 
accordance with experimental facts. 
Experimental Procedure. 
B. coli was used throughout. 
The broth employed was composed of — 
Liebig’s Extract of Meat . . 0'3 per cent. 
Salt 0-5 
Peptone TO „ 
Enumerations were made by plating out various dilutions of samples, 
taken at definite intervals of time, and counting the colonies, after 
twelve to twenty-four hours’ growth. 
Similar experiments made by Myer Coplans ( Journal of Pathology and 
Bacteriology, vol. xiv. p. 1) showed that in the early stages of multipli- 
cation a period of “ latency ” occurred, in which growth was slower than 
would be expected. We considered that this fact was not in accordance 
with the simplest experimental conditions, and attempted to eliminate it. 
For numerical study it is essential that the physical state of the organ- 
isms should be identical throughout the experiment. It was necessary 
therefore to make certain that each organism inoculated was similar in 
character to its neighbour, and also that this character was that which 
would be maintained throughout the experiment. As this condition is one 
of active growth, we therefore used for inoculation only organisms obtained 
from cultures which were already actively growing, i.e. cultures which had 
only been growing for from one to three hours. The importance of this 
point is seen on a comparison of curve 8 with curves 6 and 7. In the 
former the culture used for inoculation had been incubated for fourteen 
days, in the latter for only one hour. 
A second point of importance is that the temperature should be 
absolutely uniform throughout the whole procedure. As the taking 
of samples and their manipulation occupies at least three minutes, it is 
essential that during this period the tube should be maintained at the 
temperature of the incubator (37° C.). 
Curves 1 to 8 show the effects of improvements in the technical methods 
which we employed. 
(a) In curve l. The tubes were incubated in the air of the incubator: 
no precautions were taken to keep the tube at 37° C. during 
manipulation. 
