390 Dr. Gr. J. Stoney on the Source of the 



it of its swiftest 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 compounds. 



It is further evident that if this be the source of energy 

 upon which bacilli and cocci have to draw, the minuteness of 

 their narrowest dimension will be of advantage — probably 

 essential — to them. Presumably it would only be limited by 

 such other necessary conditions as may forbid the diminution 

 of size being carried beyond a certain point. The diameter 

 of a bacillus is frequently as small as half or a third of a 

 micron, which brings it tolerably well into the neighbourhood 

 of some molecular magnitudes. 



The transference of energy here suggested may be what 

 occurs notwithstanding that it does not comply with the 

 Second Law of Thermodynamics, which states that heat will 

 not pass from a cooler to a warmer body, unless some ade- 

 quate compensating event occurs, or has occurred, in con- 

 nexion with the transference. This law represents what 

 happens when vast numbers of molecular events (which are 

 the real events of nature) admit of being treated statistically, 

 and furnish an average result. It, therefore, Jaas its limits : 

 and the communication of energy from air to minute organ- 

 isms which is described above, is an example of a process 

 which is exempt from its operation ; since this transference 

 is supposed to be brought about by a discriminating treatment 

 of the molecules that impinge upon the bacillus of precisely 

 the same kind as that which Maxwell pictured as made by his 

 well-known demons. It therefore belongs to the recognized 

 exception to the Second Law of Thermodynamics, viz., that 

 which occurs in the few cases in which we can have under 

 observation the special consequences of selected molecular 

 events, instead of, as on all ordinary occasions, being only 

 able to measure an average outcome from all the molecular 

 events in the portion of matter we are examining. 



If some bacilli — those which live on mineral food — obtain 

 their whole stock of energy in the way here indicated, it may 

 be presumed that all bacilli get at least a part of what they 

 require in the same way. 



Should the reader have any doubt as to whether the pro- 

 cess here described is one of those that contradict the Second 

 Law of Thermodynamics, he may satisfy himself on this head 

 by the following considerations : — 



Imagine a perfect heat-engine within an adiabatic envelope 

 with some bacilli and an abundance of their mineral food, all 



