Energy required for the Life of Bacilli. 391 



being at one temperature. If events take place as supposed 

 above, the bacilli receive sufficient energy from the sur- 

 rounding medium to enable them to assimilate their mineral 

 food, and thereby to grow and multiply. Meanwhile the 

 medium becomes cooler. We may then suppose that the new 

 bacilli which have come into existence, and all the excreta, 

 are used as fuel in the heat-engine, and that its refrigerator is 

 as near as we please to being at the temperature to which the 

 medium has been reduced. The combustion of the fuel may 

 take the form of resolving the bacilli and excreta back into 

 the mineral substances from which they had been evolved, 

 except that these are now at the temperature of the combus- 

 tion. Let us next reduce this temperature in the heat-engine 

 to the temperature of the refrigerator. During this process 

 a portion of the heat may be converted into mechanical energy ; 

 and at the end of the process everything within the enclosure 

 is in the same state as at the beginning, with the sole excep- 

 tions that some of the bodies within the enclosure are now at 

 a lower temperature than at the beginning, and that the heat 

 which they have lost has been converted into mechanical 

 energy. 



It thus appears that the contents of the adiabatic envelope 

 may be regarded as a heat-engine, all the parts of which start 

 at a certain temperature, and which yields mechanical energy, 

 while the only other change is that some of its parts are cooled 

 to a lower temperature. This contradicts the Second Law of 

 Thermodynamics as formulated by Lord Kelvin, if we leave 

 the word " inanimate " out of his enunciation. His state- 

 ment of the axiom is : — " It is impossible by means of inani- 

 mate material agency, to derive mechanical effect from any 

 portion of matter by cooling it below the temperature of the 

 coldest of surrounding objects. " It is legitimate here to 

 omit the word " inanimate," as its insertion merely means 

 that cases of exception to the law may be met with in the 

 organic world ; and if this be stated it will need to be added 

 that cases of exception may also be found among inorganic 

 processes : the correct statement being that the law does not 

 apply to individual molecular events, and that therefore it 

 need not be obeyed in the cases, whether organic or inorganic, 

 in which any observable effect is the outcome of one-sided 

 molecular events. 



It should be borne in mind that the heat of a given portion 

 of matter is the energy * of motions of and within its molecules ; 



* The energy here spoken of may be partly potential : in fact while 

 motion is going on, the " energy of the motion," or a part of it, usually 

 fluctuates between being kinetic and potential, 





