120 THE HUMAN BODY. 



rupted in their course by Krause's membranes. That portion 

 of a sarcostyle, cdef, included between two consecutive mem- 

 branes is a sarcous element. The terminal portions of each 

 sarcous element are of softer consistence than most of the mid- 

 dle part and correspond to the hyaloplasm (Fig. 7) of a 

 typical primitive cell, and the material composing them may 

 be designated by the same name. The central portion of each 

 sarcous element is mainly made up of a firmer material which 

 stains with hemotoxylin and answers in general to the reticulnm 

 of a primitive cell : it is named the sarcous substance or, better, 

 the sarcosome. Each sarcosome is permeated by fine longi- 

 tudinal tubules which commence at its ends bat do not reach 

 to its centre and are thus divided into two sets by a median 

 transverse partition in which the band of Hensen lies. These 

 tubules are filled with hyaloplasm. The sarcous elements are 

 constricted where they abut on Krause's membrane and in 

 consequence each sarcostyle is narrowed at regular intervals 

 along its course. The spaces between the sarcostyles are 

 filled by a very soft sarcoplasm, which is of course more 

 abundant in the regions of Krause's membranes, where the 

 muscle-columns are constricted. In mammalian muscle the 

 sarcoplasm is present in relatively much smaller amount than 

 indicated in Fig. 58. In fresh specimens it can, however, 

 be made out in the form of fine dark lines with swollen ends, 

 lying between contiguous sarcous elements. Gold chloride 

 stains the sarcoplasm deeply but leaves the sarcostyles un- 

 colored : hence in specimens so prepared the edges or ends of 

 the sarcoplastic septa appear as very conspicuous lines, which 

 look, especially in cross-sections, as if due to a network of 

 fibres, as which they have been described by several observers, 

 and been regarded as the essential contractile part of the 

 fibre. In a relaxed muscle-fibre (A, Fig. 58) the sarcosomes 

 are comparatively long and narrow; but during contraction 

 (B) they become shorter and thicker and bulged out in the 

 middle, and more hyaloplasm passes into their tubules, which 

 become distended, especially near their deeper ends: the band 

 of Hensen also ceases to be visible. Contraction of the whole 

 fibre is thus accompanied by or, rather, is due to a transfer- 

 ence of hyaloplasm from the ends of each sarcomere into the 

 interior of the sarcosomes of its central portion, in conse- 

 quence of which the whole fibre becomes shorter and thicker. 

 The swelling of the sarcosome pushes aside some of the 



