312 INVOLUNTARY MUSCLE. [BOOK I. 



the axis of contraction 1 , overlapping their neighbours, to which 

 they are united by means of an intervening substance well seen 

 in hardened transverse sections of the tissue. The importance of 

 this interposed substance has been called in question by Engelmann' 2 . 

 In perfectly fresh specimens, not only of the ureter but also of 

 other smooth muscular tissues, it is impossible to detect any de- 

 marcation of cell from cell ; the tissue forms, to all appearance, 

 a homogeneous mass, interrupted only by the nuclei ; it is an optical 

 continuum. -This homogeneity persists, under favourable circum- 

 stances, for a short time ; but frequently, after a few minutes 

 have elapsed, fine lines begin to appear, which speedily cut up 

 the field into elongated elliptical areas, enclosing the nuclei, and 

 clearly foreshadowing the cells. Thus the homogeneity claimed 

 by Engelmann for involuntary muscular tissue is the homogeneity of 

 an absolutely fresh cornea. It is merely optical and does not imply 

 a perfect structural continuity in the sense sometimes ascribed to 

 Engelmann's words 3 . 



The cells are commonly spindleshaped, but sometimes forked and 

 flattened. They were formerly considered to possess no membrane; 

 but lately a sheath has been described, with annular swellings which 

 produce an appearance of transverse striae 4 . Their substance is 

 granular, and speckled with a varying number of refractile particles 

 soluble in alcohol; and they contain an elongated oval or rod-shaped 

 nucleus. Inside the nucleus one or more distinct nucleoli are found; 

 and beyond each pole of the nucleus, in the substance of the fibre-cell, 

 is a short row of larger granules, which diminish in size as they 

 approach the end of the fibre. The fibres frequently display a 

 longitudinal striation, especially when treated with reagents 5 ; and, 

 although they are properly described as non-striated in a transverse 

 direction 6 , yet it is no uncommon thing, when they have been 

 macerated in certain hardening fluids, to find them snapped sharply 

 across so as to leave a truncated, praemorse surface. When examined 

 with polarized light, fibre-cells, like the transversely striated muscle 



1 The power of contraction along tico axes at right angles to one another has been 

 suggested by Mr Gaskell in the case of the muscles of arterial walls. (Studies from 

 the Physiol. Lab. of the University of Cambridge, Part in. p. 164. Also Joitrn. Anat. 

 and Physiol., Vol. xi.) 



2 Engelmann, "Zur Physiologie des Ureter." Pfluger's Archiv, Vol. n., 1869, 

 pp. 247, 274. "Beitrage zur allgemeinen Muskel- u. Nervenphysiologie." Vol. in., 

 1870, p. 248. 



3 See the discussion in the Archiv f. mikrosk. Anat. by Dogiel, Foster and Dew- 

 Smith, &c. Hermann (Physiology, 2nd ed. by A. Gamgee, p. 300) so understands Engel- 

 mann : but Engelmann always refers to a physiological continuity merely, although he 

 speaks of the ureter as a ' colossal fibre.' 



4 E. Klein, "Observations on the Structure of Cells and Nuclei." Quarterly Journal 

 of Microscop. Science, New Series, July 1878, p. 331. 



5 Flemtning, "Ueber die Beschaffenheit des Zellkernes." Arch. f. mik. Anat., 

 Vol. xin. p. 693. Klein, Op. cit. 



6 See however Meissner (" Ueber das Verhalten der muskulosen Faserzellen im con- 

 trahirten Zustande." Zeitschr. f. rat. Med., 2nd Ser., Vol. n., 1858, p. 316) who saw 

 transverse markings on contracted fibres ; also Klein, Op. cit. 



