PERMEABILITY OF SURFACE LAYER OF CELLS. 2OI 



goes a corresponding sudden increase. Inhibition is to be re- 

 garded as the inverse of stimulation and as dependent on still 

 further decrease of the normal resting permeability. 



Other instances of functional increase in permeability are ap- 

 parently seen in gland cells during periods of activity. Certain 

 influences that stimulate or heighten the irritability of muscle 

 cells, as the action of pure solutions of many sodium salts, also, 

 according to Fischer's and J. B. MacCallum's researches in 

 Jacques Loeb's laboratory, 1 increase the permeability of the 

 kidney tubules and of the intestinal epithelium ; the effect is 

 checked or counteracted by the presence of calcium salts, as also 

 in the analogous case of muscular twitchings ; and according to 

 MacCallum haemolytic substances substances that increase the 

 permeability of blood corpuscles very generally exhibit a 

 diuretic action, /. c., increase the permeability of the kidney cells. 

 The fact that stimulation of a gland through its nerve, as well 

 as of a muscle, has as one of its consequences a characteristic 

 electrical variation also indicates an increase in ionic permeability 

 during stimulation. On the other hand, the recent results of 

 Asher 2 with the salivary gland and the liver do not altogether 

 bear out MacCallum's interpretation, but indicate that with such 

 cells the specific selective power or "physiological permeability" 

 is largely independent of externally induced changes in physical 

 permeability. The selective action of gland cells appears indeed 

 to be their distinctive property, and this must depend on work 

 performed by the gland cell. Nevertheless alterations in physical 

 permeability in all probability play an important role in glandu- 

 lar activity, as the conditions in the kidney indicate, although in 

 the case of glands with highly developed selective properties, as 

 the mammary gland or the liver, this factor may appear of subor- 

 dinate importance. 



In a rhythmically automatic tissue like cardiac muscle the 

 phenomena of the action-current indicate on the above theory a 

 regular alternation of periods of increased and decreased permea- 

 bility corresponding respectively to the contraction and the relaxa- 

 tion phases of the beat. Similar rhythmical changes in permea- 



1 University of California Publications, Physiology, 1904-5, Vols. I., II. 



2 Asher, loc. cit. 



