[181] I was first shown this in 1858 by the late Prof. Harless in Munich, who at the same time showed me that the nerve thus bared of its sheath, if left some hours in gastric juice, split up into regular discs, like the sarcous elements of muscles.
[182] Stieda, Bau des centralen Nervensystem der Amphibien und Reptilien, 1875, p. 41.
[183] Butzke, in Archiv für mikroskopische Anatomie, Bd. III. Heft 3, p. 596.
[184] Except in the rare cases where there is anastomosis of the muscle-fibres; as, for example, in the heart. [According to Engelmann’s remarkable researches, the muscles of the heart form a continuum, so that irritation is propagated from one to the other: Pflüger’s Archiv, 1875, p. 465. This is indubitably the case in the embryonic heart, as Eckhard pointed out.] This I hold to be the main cause of its rhythmic pulsation after removal from the body. Whatever influence the ganglia may have in exciting this pulsation, such influence would be powerless were not the muscles so connected; as may be seen in the other organs which are richly supplied with ganglia, yet do not move spontaneously; and in organs (such as the ureter or the embryonic heart, and the hearts of invertebrata) which move spontaneously, yet have no ganglia.
[185] Schröder van der Kolk, Bau und Funktionen der Med. Spinalis, p. 67.
[186] It is very instructive to learn that for some six months or so the rat is quite incapable of correctly localizing the pain.
[187] Vulpian, Leçons sur le Système Nerveux, p. 288. The experiment has been confirmed by Rosenthal, and by Bidder (Archiv für Anatomie, 1865, p. 246), who first (in 1842) attempted this union of different nerves, but arrived at negative results; as did Schiff (Lehrbuch der Physiol, 1859, p. 134) and Gluge et Thiernesse (Annales des Sciences Naturelles, 1859, p. 181).
[188] Sachs, in the Archiv für Anat., 1874, pp. 195, sq.
[189] Laplace, Essai Philos. sur les Probabilités, p. 239.
[190] The mode of termination of nerves in muscles is still a point on which histologists disagree; probably because there is no abrupt termination, but a blending of the one tissue with the other. In the Tardigrades, for example, there is actually no appreciable distinction between nerve and muscle at the point of insertion of the nerve; and if in the higher animals there is an appreciable difference between nerve and muscle, there is an inseparable blending of undifferentiated substance at their point of junction. [According to Engelmann’s recent researches, there seems good reason to suppose that muscles are composed of contractile substance and a substance which is a modification of axis-cylinder substance; the first being doubly refracting, the second isotropic: Pflüger’s Archiv, 1875, p. 432.]