MUSCULAR TWITCHINGS 759 



tive to stimuli which normally would not affect these organs. 

 For example, when we put a fresh muscle for one or more 

 minutes into a ~ solution of sodium citrate, a peculiar 

 form of irritability arises (contact-irritability). 1 Whenever 

 the muscle is taken out of the solution it goes into powerful 

 tetanic contractions, which cease at once and give way to 

 relaxation of the muscle as soon as the latter is put back into 

 the solution. When this hypersensitive condition is once 

 established, the contractions can be produced whenever the 

 muscle is changed from any aqueous solution to any other 

 non-aqueous medium, while the contractions cease when the 

 muscle is put back into an aqueous medium, no matter whether 

 the latter be a solution of an electrolyte or a non-conductor. 

 It is rather striking that these phenomena do not occur when 

 the above-mentioned solutions call forth at once the rhyth- 

 mical contractions mentioned in the previous part of this 

 paper. It almost looks as if there existed two allotropic 

 states of the muscle substance, the one giving rise to rhyth- 

 mical twitchings, the other to the peculiar tetanic contrac- 

 tions (contact-reactions) just referred to. 2 Ultimately, how- 

 ever, in all cases, rhythmical twitchings are produced. 



As far as motor nerves are concerned, I have shown in 

 the same paper that the same salts which produce this con- 

 tact-reaction produce hypersensitiveness of the nerve and 

 ultimately rhythmical contractions of the muscle when acting 

 upon the nerve alone. 



It might be mentioned here in parenthesis that these facts 

 may throw some light upon the action of cathartics. All the 

 salts which give rise to the above-mentioned contact-reaction 

 or hypersensitiveness act as cathartics when introduced into 

 the intestine. The common explanation of their action is 



i Part II, p. 692. 



2This difference is emphasized by the fact, found by my pupil, Dr. Zoethout 

 that an addition of potassium favors the contact-reaction. As far as rhythmical con- 

 tractions are concerned, K has an inhibiting effect. 



