[154] 
XII. 
SUGGESTION AS TO A POSSIBLE SOURCE OF THE 
ENERGY REQUIRED FOR THE LIFE OF BACILLI, 
AND AS TO THE CAUSE OF THEIR SMALL SIZE. 
By G. JOHNSTONE STONEY, M.A., D.Sc., F.R.S., Vice- 
President, Royal Dublin Society. 
[Read January 18; Received for publication January 20; Published 
Marcu 25, 1893.] 
Some bacilli, e.g. some of the nitrifying bacilli of the soil, are said 
to be sustained by purely mineral food. If this be the case they 
must be supplied with a considerable amount of energy to enable 
them to evolve protoplasm and the other organic compounds of 
which they consist, from these ‘materials. Now many bacilli are 
so situated that this energy is certainly not obtained from 
sunshine, and it is suggested that it may be derived from the 
gases or liquids about them. 
The average speed with which the molecules of air dart about 
is known to be nearly 500 metres per second—the velocity of a 
rifle bullet; and the velocity of some of the molecules must be 
many times this, probably five, six, or seven times as swift. We 
do not know so much about the velocities of the molecules in 
liquids.as of those in gases, but the phenomenon of evaporation 
and some others indicate that they are at least occasionally com- 
parable with those of a gas. Accordingly, whether the microbe 
derive a part of its oxygen or other nourishment from the gases, 
or from the liquids about it, it is conceivable that only the swifter 
moving molecules can penetrate the microbe sufficiently dar, or 
from some other cause are either alone or predominantly fitted to 
be assimilated by it. 
Now if this be what is actually taking place, the adjoining air 
or liquid must become cooler through the withdrawal from it of 
its swiltest molecules; and in compensation, an amount of energy 
exactly equivalent to this loss of heat is imparted to the microbes 
and available for the formation within them of organic com- 
pounds. 
