528 Dr. G. Thin on the Anatomy of 



its influence. From the broken end a large uneven mass protrudes with 

 thick everted lips, bending back over the membrane which forms a stran- 

 gulating band round the neck of the protrusion. When this sheath is 

 ruptured at different parts, the gelatinous substance, which forms a large 

 proportion of the contents of the fibre, bulges out in masses as it swells. 

 The fibrillse, which do not swell under the acid, and which are im- 

 bedded in this mass, can be often seen, in teased gold or haematoxylin 

 preparations, lying unaltered at one part of the field, while displaced 

 masses of gelatinous substance are seen at another. (It is the disposition 

 of this gelatinous substance in parallel bundles which is the cause of the 

 peculiar effect of chloride of gold, represented in figure 25, Plate XI.) 



The astringent effect of chloride of gold on the sarcolemma produces a 

 very characteristic appearance. In manipulating a fibre, as a preliminary to 

 its being hardened by gold, it sometimes happens that the membrane and 

 the layer of muscle-substance adhering to it is rent longitudinally from 

 the surface to the centre. In the gold solution it loses its cylindrical 

 form, and spreads itself out as a broad band. This perfectly flat band is 

 marked longitudinally with parallel lines, which are straight and equi- 

 distant from each other. The prolonged action of acetic acid does not 

 alter the appearance of these lines or their mutual relations, but it makes 

 visible a not very thick layer of gelatinous substance, which protrudes 

 from under the edges of the band. 



Without comparing this peculiar appearance in its most exquisite forms 

 with the transition stages sometimes seen, in which one end of a fibre 

 still retains its cylindrical form while the other end is flattened out, the 

 observer might certainly doubt that he was looking at a muscular fibre. 

 Interstices between the lines, and, in them, occasional oblong nuclei are 

 sometimes visible. 



The longitudinal lines are the optical expression of the septa between 

 the bundles, which are seen through the transparent sheath ; and that 

 the fibres in these septa are formed by elastic tissue, is shown by their 

 persistence when treated by acetic acid. 



They differ in no respect from the septa and their contained nuclei, 

 which are seen in muscular fibres that have retained their cylindrical form 

 when the chloride of gold has produced that appearance. 



Another occasional effect of the astringent action of gold is an exag- 

 geration of the dimensions of the central canal. The upturned end of a 

 fibre is sometimes seen in which there is the appearance of a wide central 

 cavity, around which the contents of the sarcolemma form a thick rim. 

 The mechanism of this appearance is explicable by the assumption that 

 the sarcolemma becomes sufficiently unyielding to form an immovable 

 surface, towards which the more yielding substance is drawn as the 

 shrinking caused by the gold proceeds. 



The sarcolemma is probably in very intimate connexion with the elastic 

 network, the more superficial cells of which, with their prolongations, are 



