FUNCTIONAL INERTIA AS LATENT PERIODS, &c. 21 



the maximum length of vagus is deducted, it 

 leaves in this case an exceedingly long physiological 

 lost time (so long in fact that this has been sus- 

 pected of being the time occupied by preparation of 

 secretin). 



Latent period exists in capillary endothelium as 

 shown in Lord Lister's early experiments on the 

 response of capillary wall to chemical and other irri- 

 tants. The wall of the vessel does not at once respond 

 to the stimulus of the mustard which at first tends 

 to make it contract, but only after an interval a 

 measure of the functional inertia of this tissue. 



The lengthening of the latent period in fatigued 

 muscle is interesting ; in fatigue, inertia is increasing 

 and one expression of this is the increase in the 

 physiological lost time. 



Vegetable protoplasm exhibits physiological 

 latency very strikingly. Mr. R. A. Robertson, 

 lecturer on Systematic Botany and Vegetable Physio- 

 logy at the University of St. Andrews, to whom I 

 had suggested seeking for examples of inertia in 

 vegetable protoplasm, writes on this point.* " A 

 change in one or more of the external conditions 

 induces a growth variation, but not all at once, 

 there is a period of non-responsiveness, of accommo- 

 dation, of anabolic inertia, and the duration of this 

 period varies with the stimulus, e.g,, the time- value 

 of the anabolic inertia is less for a temperature- 

 change than for one of oxygen-pressure or food- 



* R. A. Robertson, " On the Functional Inertia of Plant Proto- 

 plasm." P. R.S.E., Session 1901-1902. Vol. xxiv. Part iii. 



