THE VITAL PHENOMENA OF CELLS 



47 



himself justified in concluding that animals have a peculiar kind of elec- 

 tricity and that it is of very great importance in the functions of the animal 

 body; in fact, physiologists of that time thought their dream of a vital force 

 was at last to be realized. 



It was reserved for the discriminating insight of Volta to show that these 

 contractions are conditioned upon the dissimilarity of the two ends of the 

 metal touching the moist conductor, and upon the production thereby of a 

 galvanic arc. Further investigation proved, however, that electrical differ- 

 ences of potential do occur in the animal body. The events historically most 

 important from this point of view are: the discovery of the so-called frog 

 current i. e., of a current running from the feet to the head of the frog 

 (Nobili, 1827) ; the demonstration that the isolated muscle under definite 

 circumstances gives a regular current (Matteuci and Du Bois-Reymond, 

 1840-1843); the discovery of the electrical variations in muscular activity 



FIG. 29. Schema representing the current of injury, or demarcation current, in a muscle, after 



Foster. 



(Matteuci and Du Bois-Reymond, 1842) ; and the discovery of the nerve 

 current and its variations (Du Bois-Reymond, 1843). 



The object most used in these investigations is cross-striated muscle. If 

 two points of an exsected muscle be connected with a galvanometer an excur- 

 sion of the needle nearly always occurs ; between the two points of the muscle 

 there is, therefore, a difference in tension. More detailed study has shown that 

 these tension differences are perfectly regular, and in muscles with parallel 

 fibers they have been found to take the following form (Du Bois-Reymond) 

 (cf. the schema in Fig. 29). If a longitudinal surface and a transversely cut 

 surface of such a muscle be connected with a galvanometer, a current is 

 obtained, which in the muscle is directed from the transverse to the longi- 

 tudinal surface, and which reaches its greatest intensity (0.06 to 0.08 volt) 

 if the leading-off electrodes are placed in the middle of the two surfaces. 

 If two asymmetrical points of the longitudinal surface be led off weaker cur- 

 rents are obtained, which in the muscle are directed from the periphery 

 toward the middle. With two asymmetrical points of the cross section a 

 current is obtained which passes from the middle toward the periphery. 

 Finally, if symmetrical points of the cross section or of the longitudinal sur- 



