ARTIFICIAL RHYTHM. 191 



rhythm as due to a constant chemical stimulus, 

 I studied it with much care, and shall now give 

 a full description of what appears to me an im- 

 portant body of physiological facts. 



Ten to twenty drops of acetic acid having been 

 added to one thousand cubic centimetres of sea- 

 water, and the paralyzed bell of Sarsia having been 

 placed in the mixture, an interval of about half a 

 minute will elapse before any movement begins. 

 Sooner or later, however, the artificial rhythm is 

 6ure to be induced, and it will then continue for 

 a variable time — occasionally as long as an hour, 

 and generally for a considerable number of minutes. 

 After it ceases it may often be made to recommence, 

 either by adding a few more drops of acid to the 

 sea-water, or by supplying an additional stimulus 

 to the bell by nipping it with the forceps. Even- 

 tually, however, all movement ceases, owing to the 

 destruction of irritability by the action of the acid. 

 By this time the whole inner surface of the bell has 

 become strongly opalescent, owing to the destruc- 

 tive influence of the acid on the epithelial cells 

 which overspread the irritable tissues. The latter 

 fact is worth men'-ioning, because in no case does 

 the artificial rhythm set in until this opalescence 

 has begun to show itself ; and as this opalescence 

 is but an optical expression of the damage which 

 the epithelial coat is undergoing, the explanation of 

 the time which elapses after the first immersion 

 of the bell in the acidulated water and the com- 

 mencement of the artificial rhythm no doubt is, 

 that duri])g this time the acid has not obtained 



