PHYSICAL METHODS IN PHYSIOLOGY 85 



an individual treatment of the particles, molecules, and atoms, 

 and on those physical generalisations which are true not only 

 of the mass, but of the units composing it. If this line of 

 reasoning be correct, all kinds of interesting speculations arise 

 as to the behaviour of a system in which the statistical rules 

 do not apply, and it may be possible some day, by direct 

 experiment on living creatures, to prove or disprove the 

 applicability of such rules. If, for example, a living cell were 

 shown to provide at constant temperature more free electrical, 

 or mechanical, energy than was accounted for by the free 

 energy of the food-stuff used, it would be evading a statistical 

 rule, the Second Law of Thermodynamics. This possibility 

 may seem far-fetched, and it is probably better — as a matter 

 of expediency, until the assumption is disproved — to assume 

 that the statistical rules of the exact sciences do apply to 

 the living cell with the same rigidity as do the laws of a 

 more general nature. But it will be wise to bear in mind 

 that possibly the fundamental difference between the living 

 and the non-living world — a difference obvious enough, though 

 difficult to fit into a mechanistic philosophy — may be simply 

 that the statistical rules governing the non-living, i.e. the non- 

 organised, do not necessarily, and under all conditions, apply 

 to the minute organised mechanisms employed by the living 

 cell. We are reduced, therefore, by these considerations also to 

 a study of the individual properties of the particle or molecule, 

 as the means whereby physiology is most likely to advance 

 along physical lines. 



The living tissues of whose physical and chemical properties 

 — in relation to function — we know most are the striated muscle 

 cell and the medullated nerve fibre. There is no peculiar 

 virtue in the investigation of these tissues, except that — more 

 than others — they allow one to obey the foremost of all working 

 rules and to " isolate one's variables." Generations of physio- 

 logists have applied themselves to the investigation of the 

 properties of muscle and nerve, following a sure scientific 

 instinct, for with these highly differentiated cells, showing 

 sharply defined physical characters, it is possible to isolate one's 

 variables and to investigate them separately in a manner quite 

 impossible in what some people regard as the simpler " general 

 utility " cell. In many respects all living cells behave according 

 to the same general rules, and the relations established for 

 muscle and nerve may often be applied, mutatis mutandis , to 

 other cells and organs. For example, it has been shown that a 

 muscle, when excited, liberates energy from a " ready store " 

 of some kind, using oxygen only in the slower and secondary 

 processes of " recovery." This general statement probably 

 applies to the conduct of all living cells. Or, again, the excita- 



