PHYSIOLOGY. 



671 



a nerve in preventing the passage of nerve- 

 force, while not interfering with the flow of 

 electricity. The electrical phenomena connect- 

 ed with the activity of nerves appear, there- 

 fore, to be secondary in their character, and 

 not to constitute the essential process in nerve 

 action. In studying the nature of nerve-force, 

 two alternatives present themselves. We may 

 conceive the impulse to be conducted through 

 the nerve-fiber by a series of retrograde chem- 

 ical changes in the successive molecules of the 

 nerve substance, or we may suppose it to be 

 transmitted from molecule to molecule by some 

 sort of vibratory action. As the former theory 

 involves the supposition of a using up of or- 

 ganic material and the consequent discharge 

 of potential energy in the successive portions 

 of the nerve, it may be called "the discharg- 

 ing hypothesis." The second theory, implying 

 simply the transferring of motion, may be called 

 "the kinetic hypothesis." If the discharging 

 hypothesis be correct, we may reasonably ex- 

 pect to find in the active nerve-fiber evidences 

 of chemical decomposition and of heat-produc- 

 tion ; and, as under it the organic substances 

 are used up faster than they are replaced or 

 their products of decomposition removed, we 

 may expect to observe a diminution of nerve- 

 action during the continuance of the stimula- 

 tion, or the phenomena of fatigue. Experi- 

 ments indicate that none of these phenomena 

 show consumption of organic substance. They 

 are, therefore, so far not favorable to a dis- 

 charging theory, and are, by implication, more 

 favorable to the kinetic theory. 



An electric chronometer has been employed 

 by Dr. D' Arson val for the direct measurement 

 of the speed with which nervous impressions are 

 conveyed. On application of the instrument 

 to the body, circuit is broken, and a pointer 

 begins to travel. On feeling the sensation the 

 patient touches a button, which restores circuit 

 and stops the pointer. The interval can then 

 be determined within hundredths of a second. 

 Experiments with the instrument show that 

 different sensations are transmitted with differ- 

 ent velocities, and that different diseases abolish 

 some while exalting others. 



Remarking on the degeneration of nerves 

 resulting from sectional injury, Dr. Prause says 

 that, according to Waller, when a nerve is cut 

 through the peripheral parts degenerate, where- 

 as the central remain intact. The result of a 

 thorough investigation of the nerves in cases 

 of amputation, which the author had carried 

 on some years ago in conjunction with Dr. 

 Friedlander, had, however, shown that the 

 central parts of the divided nerves had degener- 

 ated up to the spinal cord. In a case where, 

 on account of gangrene of the foot, the leg had 

 been amputated close below the knee, the de- 

 generation of the nerves, having started from 

 the gangrenous parts and progressed centripe- 

 tally, had extended up to and probably beyond 

 the surface of amputation. Side by side, how- 

 ever, with the larger number of degenerated 



fibers a few normal fibers were found. From 

 experiments on animals in which nerves of 

 very different kinds, both sensory and mixed, 

 were cut through, it appeared that in the 

 peripheral parts by far the larger number of 

 the fibers degenerate, while at the same time a 

 not inconsiderable number remain unaltered. 

 Similarly degenerated and normal fibers were 

 found in the central part of the nerve, only in 

 this case the relative number of each kind 10 

 an inverse proportion to that in which they 

 are found in the peripheral part. It follows 

 from the above that, starting from the point 

 of section of a nerve, one set of fibers de- 

 generates toward the periphery, the other 

 toward the center. It seemed right to assume 

 that those fibers which degenerate toward the 

 periphery have their trophic center in the spi- 

 nal cord or brain, as the case may be, while 

 those which degenerate centripetally are de- 

 pendent for their nutrition on some center at 

 the periphery, such as, presumably, the tactile 

 corpuscles of Meissner. Were this not so, Wal- 

 ler's law would again hold good, since only 

 those parts of a nerve degenerate which are cut 

 off from their trophic center; only sensory 

 nerves degenerate centripetally. 



Experiments have been made by Dr. Raske 

 with the co-operation of Dr. Kossel, on the 

 chemical composition of the brains of the em- 

 embryos of horned cattle, in order to determine 

 whether it or morphological structure is pri- 

 mary during the process of development. The 

 values found in two brains were compared 

 with the results of the chemical investigation 

 of brains which had been carried out in the 

 laboratory of Prof. Hoppe Seyler, whose in- 

 vestigations had shown that the gray substance 

 of the brain of full-grown cattle differs essen- 

 tially from the white substance, by containing 

 but little, if any, cerebrine, a less amount of 

 cholesterine, and a greater quantity of albu- 

 men and extractives than the latter. In these 

 particulars, the brains of the embryos of 

 horned cattle hold exactly the same posi- 

 tion as does the gray substance of grown-up 

 brains. It was only in the quantity of lecithine 

 and of salts that the embryonal brains demon- 

 strated any difference from the gray substance. 

 The embryonal brain is, therefore, very essen- 

 tially distinguished from the white substance 

 a phenomenon which is in harmony with the 

 fact that, in the embryonal brain medullated 

 nerve-fibers were not met with. 



From an investigation of the histology and 

 function of the mammalian cervical ganglion, 

 in which a large number of specimens hu- 

 man, other mammalian, and fetal were ex- 

 amined, W. Hale White concludes that human 

 adult ganglia vary as much in size as do the 

 largest and smallest of other mammals, and 

 that the size of the ganglion in other mam- 

 mals varies directly as the size of the animal ; 

 that human superior cervical ganglia present 

 granular pigmented atrophied cells much more 

 frequently than those of other mammals ; that 



