MEMBRANE CHANGES DURING STIMULATION 365 



the thermionic amplifier to enhance the minute effects 

 obtainable from single eggs, and the string gal\-anomctcr 

 as the recording instrument. It should be noted, 

 however, that Miss Hyde's observations are in conformity 

 with those of other investigators who have found rapidly 

 growing regions of plants and animals— i.e., those where 

 cell-division is in active progress — to be electrically 

 negative to more slowly growing regions.' 



Evidence that reversible variations of permeability 

 are associated with such processes as fertilization and cell- 

 division may seem to have a somewhat indirect bearing on 

 the problem of the conditions of stimulation in t}^)ical ir- 

 ritable tissues hke muscle and ner\'e. Yet all of these vital 

 processes are alike in being subject to initiation or control 

 by environmental conditions or events; in other words, 

 they all illustrate the characteristic ''irritability" of 

 living matter. The fundamental conditions determining 

 and controlling the metabolic reactions which furnish 

 the energy for vital processes are in all probability every- 

 where the same. Hence the above-cited facts indicating 

 that changes of permeabihty are regular accompaniments 

 of fertilization and cell-division are confirmatory evidence 

 for the view that such changes play an essential part in 

 other manifestations of irritability. In all forms of 

 protoplasm the essential metabolic reactions occur 

 under the control of the film-partitioned or emulsion-like 

 structure of the living system; it is therefore to be 

 expected that they will vary in their rate and character 



»Cf. Hermann and Muller-Hcttlingcn, Arch. gcs. Physiol., XXXI 

 (1883), 193; A. P. Mathews, American Journal of Physiology, VIII 

 (1903), 294; C. M. Child, Biological Bulletin, XL! (1921), 9°; t- J- 

 Lund, Journal of Experimental Zoology, XXXVI (19"), 477; Hyman 

 and Bellamy, Biological Bulletin, XLIII (192^), 3U- 



