638 ELECTRO-PHYSIOLOGY. 



which is present in dead muscles, can be demonstrated, though not con- 

 stantly, in dead nerves. 



The functions of the brain cease immediately after the onset of death, as 

 indicated by loss of consciousness and cessation of perceptive activity; so that 

 reports of brain-activity after decapitation are to be relegated to the realms of 

 fable. The vital functions of the spinal cord, however, persist for a somewhat 

 longer time, particularly those of the white substance. Death occurs next in the 

 large nerve-trunks ; then in the nerves for the extensors and in those for the flexors 

 (in three or four hours) . The sympathetic fibers retain their irritability longest (up 

 to ten hours in the intestine). The irritability of the nerves of frogs can be pre- 

 served for several days in the dead body if kept in the cold. 



The irritability of the peripheral stumps of divided nerves is lost in pigeons 

 and rodents in from two to three days; in hoofed animals in from eight to ten 

 days; in other warm-blooded animals in four days. In mixed nerves death of 

 the fibers takes place at different intervals; for example, in the vagus, of the 

 inhibitory fibers first, later of the accelerator fibers for the heart. The stumps of 

 the cerebral nerves retain their irritability for a longer time than do those of 

 the spinal nerves. 



ELECTRO-PHYSIOLOGY. 



The discussion of electrical phenomena will be preceded by a concise summary 

 of the necessary preliminary physical considerations, without which a comprehen- 

 sion of the subject is impossible. This presentation will be made in a connected 

 manner, the apparatus and methods devised for electro-physiological and electro- 

 therapeutic purposes being described in their proper place. The student should 

 familiarize himself thoroughly with this preliminary knowledge of physics. 



PRELIMINARY PHYSICAL CONSIDERATIONS. THE GALVANIC 



CURRENT. 



ELECTROMOTORS. CONDUCTION-RESISTANCE. OHM'S LAW. CONDUC- 

 TION THROUGH ANIMAL TISSUES. THE RHEOCORD. 



If two of the bodies named later on are brought into direct contact with 

 each other, positive electricity will be appreciable in the one and negative electricity 

 in the other. The cause of this phenomenon is the electromotive force, which 

 causes positive electricity to pass into the one body and negative electricity into 

 the other. In accordance with the relations of the bodies to be discussed later 

 on these are divided into conductors and non-conductors, and the conductors again 

 into those of the first and those of the second class. 



Conductors of the first class, chiefly the metals, can be arranged in such a 

 series (tension-series) that, on contact of the first mentioned with one of the 

 succeeding members of the series, the first body becomes electrically negative and 

 the last positive. This tension-series is: Manganese, carbon, platinum, gold, silver, 

 copper, iron, tin, lead, zinc. The intensity of the electrical excitation resulting 

 from the contact of two of these bodies is the greater the farther the bodies are 

 separated from each other in this tension-series. The contact of the bodies may 

 take place indifferently at one or at several points. If several of the bodies in 

 the tension-series are placed one upon the other, the electrical tension thus induced 

 is the same as if the two terminal bodies alone were brought in contact, with omis- 

 sion of the intervening bodies. 



If, on the other hand, conductors of the first and the second class are brought 

 in contact, the result is different. Zinc in contact with water is strongly negative, 

 the fluid positive. Zinc in contact with diluted acids is likewise negative, while 

 other metals, such as copper and platinum, are less actively negative or even 

 positive. 



Experience has shown that those metals in contact with a fluid become in 

 strongest degree electrically negative that are chemically most strongly acted upon 

 by the fluid. Every combination, however, exhibits a constant difference in ten- 

 sion or potential. The density of the amounts of electricity set free from both 



