July 29, 1921] 



SCIENCE 



91 



striking, but the demonstration of electrical 

 currents in the human body would be usually 

 regarded as impossible without a galvanom- 

 eter. These difficulties are solved by the rather 

 simple experiments cited below. 



Recently^ while making a jierve muscle 

 preparation, the thigh muscles of the left leg 

 of the frog were removed and the nerve on the 

 same side isolated but not sectioned. The 

 body was well moistened with physiological 

 saline and lay on a glass plate which was also 

 well moistened. The toes of the left foot 

 were held in the left hand, while forceps, held 

 in the right hand, were accidentally placed 

 upon the body of the frog. Immediately a 

 violent contraction of the muscles of the left 

 leg occurred. This was so unusual that we 

 investigated this further. The same results 

 were obtained repeatedly. It must be noted 

 here that one metal was used instead of two 

 as in Galvani's experiment, and in place of 

 the other metal the human hand was used. 

 The current stimulating the nerve might have 

 been due to the difference in potential between 

 the metal and the hand, and for that reason 

 we substituted the right finger for the metal 

 previously used and obtained the same results. 

 We therefore concluded that the nerve was 

 stimulated by the action current of the human 

 body, the electrodes being the fingers of the 

 right and left hands and the indicator or the 

 galvanometer being the contractions of the 

 frog's muscles. 



The same experiment was tried on a number 

 of frogs and in every case we obtained the 

 same results, although more striking in some 

 preparations than in others. We found that 

 by making contact with any part of the frog's 

 body or even the saline solution on the plate 

 the muscles contracted. 



When a non-conductor was interposed be- 

 tween the toes and the hand we found that no 

 contraction took place. When a non-con- 

 ductor such as wood was used for the right 

 electrode no contraction took place. We at 

 first thought that the action current involved 

 was that produced by the beating human heart, 

 but the absence of the rhythmical contractions 

 in the muscles of the frog negates this. 



It has been noted in some cases that the 

 contractions were very violent, even tetanic, 

 and i mm ediately afterwards hardly noticeable. 

 We have no explanation to offer for this 

 other than the varying electrical currents in 

 the body. 



George G. Scott, 

 Joseph Tulgan 

 Dept. op Biology, 

 College of the City op New Yoke 



an exception to dollo's law of the ir- 

 reversibility of evolution 



It has been claimed that most cases of ap- 

 parent reversion to a primitive type in spe- 

 cialized organisms — such as the occurrence of 

 three toes in the horse that Csesar rode, or a 

 reversion to the primitive number of petals in 

 flowers, etc. — are to be explained simply as ad- 

 ditions of supernumerary parts, comparable to 

 polydactylism, or the addition of supernumer- 

 ary digits to those normally present in man, 

 cats, etc. Since so many cases of an apparent 

 reversing of the evolutionary process appar- 

 ently have to do with the number of the va- 

 rious structural features present, and are 

 therefore open to the objection that we may 

 be dealing with merely an addition of super- 

 numerary parts to those normally present, it 

 may be of some interest to cite a clear case 

 of reversion to the primitive condition in 

 structures in which there can be no possible 

 question of the addition of supernumerary 

 parts. 



In the fruit fly Drosophila, as is true of 

 practically all Diptera, there has been such a 

 marked specialization of the metathoracic re- 

 gion that the sclerites of this segment of the 

 thorax have been profoundly modified and 

 reduced, especially in the tergal region; and 

 the metathoracic wings have been reduced to 

 mere knobbed threads, the halteres, which 

 would not be recognized as the vestiges of 

 wings, if we did not know that they are 

 modified wings from their mode of develop- 

 ment, etc. Dr. Morgan, however, has recorded 

 a mutant of Drosophila which he describes as 

 having a " double thorax," apparently not re- 

 alizing the true nature of the parts in the 



