IS© THE POPULAR SCIENCE MONTHLY 



ride solution on the pigment-containing cells of this organism; at the 

 same time they decrease or prevent the stimulating action of this solu- 

 tion. They also protect the organism against its toxic action, as we 

 have already seen. An anesthetic action is thus the equivalent of both 

 an anti-stimulating and an anti-cytolytic action. Both effects depend 

 upon a modification of the plasma-membrane; under the influence of 

 the anesthetic this structure becomes more resistant than normally to 

 conditions that otherwise increase its permeability. We may infer in 

 general that the degree of responsiveness of an irritable tissue is 

 dependent on the state of its plasma-membranes; and that anesthesia 

 corresponds to a condition of decreased susceptibility, and hyper- 

 irritability to one of increased susceptibility, to the action of per- 

 meability-increasing agencies. Sensitization and desensitization, on 

 this view, are primarily surface effects, dependent on alteration of the 

 limiting membranes. 



The polarization-changes accompanying stimulation may be ex- 

 tremely rapid in some cases. During the contraction of a man's vol- 

 untary muscle under the influence of the will, the existence of a 

 rhythmical electrical variation with an average rhythm of about fifty 

 vibrations per second has recently been demonstrated by the thread-gal- 

 vanometer. The negative variation accompanying a single muscular 

 twitch occupies from one hundredth to one two-hundredths of a second 

 in a frog's voluntary muscle at ordinary temperatures ; that accompany- 

 ing a single nerve impulse lasts about one thousandth of a second ; 

 while more slowly reacting tissues, like heart-muscle or smooth muscle, 

 show correspondingly slower electrical variations. On the membrane- 

 theory the corresponding permeability-changes in the membrane must 

 occupy similar times; and this consideration indicates the extreme 

 delicacy of the adjustment between permeability and electrical polariza- 

 tion that must exist in the membranes of highly irritable tissues. 



The electrical phenomena of stimulation are, however, relatively 

 inconspicuous — if we except the case of the electric eel or torpedo. 

 The characteristic and biologically important " response " of the tissue 

 varies with its special nature. A muscle contracts, for instance; a 

 gland secretes. The relation between the rapid change of polarization, 

 which is the primary event in stimulation, and the resulting mechanical 

 and chemical effects remains to be inquired into. The problem is a 

 difficult one, and insufficiently investigated. The energy of muscular 

 contraction is derived from the oxidation of energy-yielding compounds, 

 like sugar. We must conclude that the polarization-changes at the 

 cell-surface influence the chemical processes in the muscle-cell. Stim- 

 ulation is known to increase many times the rate of oxidation in muscle- 

 cells. I have lately attempted to modify the rate of formation of indo- 

 phenol (a deeply colored organic oxidation-product) in the blood cor- 



