PERMEABILITY OF SURFACE LAYER OF CEILS. 1 99 



Hence the haemolytic action of many toxins: the injury to the 

 plasma-membranes is naturally not confined to the blood cor- 

 puscles the effect is merely most plainly evident in these cells ; 

 but all or most of the cells of the organism are to be regarded as 

 similarly affected. 



The above substances produce irreversible or toxic changes in 

 cells by influencing through their chemical or solvent or coagu- 

 lative action the permeability of the plasma-membrane. Essen- 

 tially similar effects may result in many cases from moderate rise 

 of temperature. Thus exposure of frog's muscle to temperatures 

 approaching 40 for a short time produces the typical phenome- 

 non known as heat-rigor, in which the muscle shortens and 

 thickens while its substance undergoes complete coagulation and 

 acquires a pronounced acid reaction. A closely similar change 

 results when a muscle is immersed in a saturated solution of a 

 lipoid-solvent like chloroform in an indifferent medium (e. g., 

 Ringer's solution). In both cases the changes in the muscle are 

 associated with a loss of semi-permeability and of electrical polari- 

 zation ; and they are almost undoubtedly direct consequences of 

 this since neither the moderate rise of temperature nor the pres- 

 ence of chloroform has by itself any such coagulative effect on 

 the colloids composing the muscle substance ; while loss of semi- 

 permeability, with consequent disturbance of chemical equilibrium 

 and production of acids, may readily produce just such effects. 1 

 Why such moderate heat should so profoundly alter the proper- 

 ties of the plasma-membrane is not evident at first sight ; possi- 

 bly the colloidal aggregation-state is the condition immediately 

 influenced by the change of temperature ; possibly the primary 

 effect is a chemical one. 



The above are instances of artificially produced or pathological 

 changes in permeability. Normal or functional changes in this 

 property appear to be of frequent occurrence in living organ- 

 isms. Thus there is highly conclusive evidence that the general 

 process of stimulation is dependent on a temporary and reversible 

 increase in permeability. Very clear indications of this kind are 



1 Compare my former paper, American Journal of Physiology, 1908, XXIT., pp. 

 81-83. Vernon, Journal of Physiology, 1899, XXIV'., p. 239, and Meigs, Arner. 

 Jottrn. Physiol., 1909, XXIV., p. 178, also regard heat-rigor as having no direct 

 connection with the heat coagulation of the proteins of muscle. 



