434 SPECIAL HISTOLOGY. 



similar mechanical function appears to me to be performed by tlie fine 

 granular substance, which in the higher central organs is found in so 

 many situations supporting the most delicate nerve-fibres, cells, and 

 processes. 



With respect to the methods to be employed in investiyations of the 

 nervous system, the principal have been noticed in the preceding sec- 

 tions. I will, here, once more advert to the importance of preparations 

 made with chromic acid in the investigation of the course of the fibres, 

 and in the examination of the central nerve-cells ; and direct attention 

 to the dilute solution of caustic soda for the detecting of nerve-fibres in 

 non-transparent tissues, — without which two means very many points 

 would remain in the dark. In this way also the extreme proneness to 

 become changed, of the gray and white substances, and particularly the 

 ready disruption of the processes of the nerve-cells, and the varicosity, 

 coagulation, and destruction of the nerve-fibres, are at once removed or 

 avoided. The brain and spinal cord, as well as the elements of the 

 ganglia, are best studied in the human subject, but the course of the 

 fibres in them, and, above all, the terminations of the nerves, are best 

 investigated in the smaller Mammalia, and only in the second place in 

 Man. In the searching for the minute ganglia in the heart, Ludwig 

 recommends the treatment with phosphoric acid and the solution of iodine 

 in hydriodic acid, the latter so diluted that it has only a tinge of brown. 

 For the development of the nerves, the human and mammalian embryo 

 are quite suitable ; but the batrachian larvse, and if opportunity ofi'er, 

 the electric organs of the embryo Ray, in which the conditions are by 

 far the most clearly displayed, should not be overlooked. 



Literature of the Nervous System. — C. G. Ehrenberg, " Beobachtung 

 einer bisher unbekannten Structur des Seelenorgans des Menschen" 

 (Observation of a hitherto unknown structure in the Human Brain), 

 Berlin, 1836; G. Valentin, in Mlill. "Archiv," 1839, p. 139, 1840, p. 

 218, in Valentin's " Repertorium," 1838, p. 77, 1840, p. 79, 1841, p. 

 96, 1843, p. 96, and: " Hirn- und Nervenlehre" (Treatise on the Brain 

 and Nerves), Leipzic, 1841 ; J. E. Purkinje, in the "Bericht liber die 

 Versammlung deutscher Naturforscher," in Prague, for the year 1837, 

 Prague, 1838, p. 177, and in Mlill. " Archiv," 1845, p. 281 ; R. Remak, 

 in Mull. "Archiv," 1841, p. 506, 1844, p. 461, " Ueb. ein selbstandiges 

 Darmnervensystem" (On an independent system of intestinal nerves), 

 Berlin, 1847; J. F. Rosenthal, '•'' De formatione granulosa in nervis 

 aliisque ijartihus organismi anijnalis," VratisL, 1839 ; A. W. Volk- 

 mann, in Mull. "Archiv," 1838, p. 274, and 1840, p. 510; Artie. 

 "Nervenphysiologie," in Wagner's " Handw. der Phys.," II.; F. H. 

 Bidder and A. W. Volkmann, " Die Selbstandigkeit des sympathischen 

 Nervensy stems durch anatomische Untersuchungen nachgewiesen" (The 



