458 PHYSIOLOGICAL REGULATIONS 



(4) Factors of safety. In a broad way, a factor of safety 

 appears to refer to any provision that increases survival (Meltzer, 

 '07). In engineering parlance it is a ratio between that which 

 occurs and that which could occur without destruction. In a liv- 

 ing unit it might compare either maximum and minimum (as in 

 modification ratio), or content at tolerated load and content at zero 

 load. All equilibration diagrams express factors of safety and 

 furnish quantitative data corresponding to each definition, since 

 each component is represented both in rates and in loads. No 

 doubt every physiological property is insured by factors of safety 

 of some sort. 



Speculations concerning maxima, minima, capacities, safety, 

 and economy bear strong metaphysical connotations at the same 

 time that they bear the stamp of mathematical exactitude. The 

 connotations largely disappear when one has the data in quanti- 

 tative form. For then a minimum means no more than a point on 

 a curve, and a factor is a defined relation between two points. The 

 speculations are uncalled for as soon as definitions are set up, and 

 data are obtained to correspond to those definitions. 



§ 167. Origins of equilibrations 



Means of expressing certain physiological patterns (equilibra- 

 tions) having been found, it is a temptation to examine the patterns 

 successively in the many connections that anatomical patterns are 

 commonly regarded. Among those aspects, the ontogeny and 

 phytogeny of function have received a share of speculation; per- 

 haps the present quantitative data suggest further ones. 



In ontogeny the clearest data seem to be those of heat equili- 

 bration. In rabbit (fig. 151), mouse (Pembrey, 1895), and wren 

 (Kendeigh, '39) a series of progressive changes appears in the 

 equilibration diagram for heat. At birth nearly the same rates 

 of heat production and coefficients of heat loss prevail at all body 

 temperatures (heat contents) in those species. But gradually the 

 rate of heat production "differentiates" so as to correlate nega- 

 tively with heat content, and the rate of loss to correlate positively. 

 No doubt a great variety of sensory and coordinative links take part 

 in this differentiation. 



The individual organism starts life in a relatively isolated state. 

 Partial isolation is what the parent organism provides ; it tides the 

 organism over the period when its functions are being acquired. 



