Nature of Chemical Stimulation. 



173 



for a definite period to the sensitizing (or desensitizing) solution, 

 e. g., is placed for four minutes in m/8 NaBr, from which it is 

 transferred directly to the stimulating solution; the response, if 

 sensitization has occurred, is found to be more energetic than 

 before; if desensitization has occurred, it is lessened or abolished. 



The relative sensitizing powers of a series of sodium salts have 

 been thus determined, using the following solutions as stimuli: 



1. m/8 KC1. 



2. Isotonic solutions of sodium salts containing potassium (to 

 increase the twitching effect), e. g., 7 vols, m/8 Nal + 1 vol. m/8 

 KI. 



3. Pure isotonic solutions of sodium salts which produce active 

 twitching: acetate, sulphate, tartrate, citrate. 



4. Saturated solution of a typical lipoid solvent, chloroform, in 

 Ringer's solution. 



5. Solution of a typical hemolytic, 0.2 per cent, saponin, in 

 Ringer's solution. 



All of these solutions produce contraction in fresh normal mus- 

 cle. The response is typically and often markedly increased after 

 treatment with pure solutions of sodium salts, especially sodium 

 nitrate, sodium chlorate, sodium sulpho-cyanate and sodium io- 

 dide. Magnesium and calcium chlorides, on the other hand, de- 

 crease the response to all salts, but not to chloroform or saponin. 

 A difference thus appears according to whether the stimulating 

 solution has a general action on colloids, or affects primarily the 

 lipoids. 



The order of relative sensitizing action for isotonic solutions 

 of the following sodium salts is, in general, as follows: NaCl < 

 NaBr < NaN0 3 < NaC10 3 < Nal and NaCNS. This statement 

 applies more particularly to stimuli (1), (2), (4) and (5); the salts 

 in group (3), especially sulphate, tartrate and citrate (which appear 

 to act by lowering the concentration of Ca-ions) show somewhat 

 different relations. The above order corresponds to the order of 

 relative action on colloids, and indicates that the salts increase 

 irritability by altering, in the direction of increased dispersion, the 

 state of subdivision of the colloidal constituents of the plasma- 

 membrane. The desensitizing or anesthetic action of the alkali- 

 earth chlorides is presumably dependent on an alteration of the 

 plasma-membrane colloids in the reverse direction. 



