172 



Scientific Proceedings (39). 



after return to the indifferent medium; loss of irritability accom- 

 panies the contraction, which is also associated with a coagulation 

 indistinguishable from that of death rigor. In spite of the external 

 differences between the two types of contraction, there is evidence 

 that their fundamental conditions are identical, and that the irre- 

 versibility of the second type depends simply on the irreversibility 

 of the change in the plasma-membrane. The latter loses its vital 

 semi-permeability temporarily in the first, and permanently in the 

 second case; the loss of irritability and the coincident rigor or 

 contracture are consequences of this permanent loss of the normal 

 condition of semi-permeability. 



The distinction between reversibility and irreversibility in the 

 stimulating action of salts undoubtedly has as its ground the 

 similar distinction in the action of salts on the aggregation-state 

 of proteins. Alkali and alkali-earth neutral salts produce reversible 

 changes in the colloidal aggregation-state, while with heavy metal 

 salts the aggregation-changes are irreversible (Pauli). In cor- 

 respondence with this difference, it is found that the stimulating 

 (or inhibiting) effects produced by the first group of salts are 

 reversible, while those produced by the second are irreversible. 

 In the case of lipoid-solvents in strong solution (which also produce 

 contracture passing into rigor) it is to be assumed that the 

 lipoids in the plasma-membrane undergo a change of state too 

 far-reaching to be reversible (dissolving out, etc.). Hemolytics 

 and other poisons must be assumed to act by virtue of various 

 special peculiarities; thus saponin, e. g., probably alters the con- 

 dition of the cholesterin and so destroys the semi-permeability 

 of the membrane. 



In the following experiments the sensitizing and desensitizing 

 action of various electrolytes has been studied in relation to the 

 above different forms of chemical stimulation. Frog's gastrocne- 

 mii have been chiefly used. The muscle, arranged to write on a 

 drum, is brought from Ringer's solution into the stimulating solu- 

 tion (where it contracts, describing a curve) ; after a definite inter- 

 val (1 to 2 minutes) it is returned to Ringer; relaxation may or 

 may not follow, according to the character of the stimulus. The 

 same muscle (if reversible stimulation is used), or the other muscle 

 of the same animal (with irreversible stimulation), is then exposed 



