QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 191 



bright, slightly refractive band — isotropous substance ; so 

 that each division contains, between the two intermediate 

 discs, one median disc, two transverse discs, then two isotro- 

 pous bands, two lateral discs, and finally again two isotropous 

 bands. 



"a. The intermediate disc, or the membrane of Krause, is 

 distinctly to be recognised as a separate structure in the per- 

 fectly fresh fibre in the state of rest, when examined without 

 a reagent, and if the height of a muscular division exceeds 

 0008th part of a millimetre. In those cases where the 

 lateral disc is very dark, and is in close contact with the 

 intermediate disc, this latter may easily escape observation ; 

 it can, however, be brought into view by slightly stretching 

 the muscular fibre. The intermediate disc appears under the 

 microscope as a single dark line, being a homogeneous, highly 

 refractive membrane ; it is very elastic, and, when observed 

 in polarised light, in preparations that have been hardened 

 in alcohol or osmic acid, and mounted in dammar, dis- 

 tinctly anisotropous. 



" b. The isotropous thin band being at the side of the 

 intermediate disc is in fresh fibres only recognisable when 

 the height of a muscular division amounts to O'OOSth of a 

 millimetre and more. Otherwise the lateral disc seems to be 

 in contact with the intermediate disc. In this latter case the 

 isotropous band can be brought into view by adding one per 

 cent, of acetic acid, which causes the isotropous band to swell 

 on and be perceptible. 



" c. The lateral disc is in the fresh fibre always darker than 

 the isotropous band ; it is seldom homogeneous, commonly 

 granular. The granules are generally of equal size, and iso- 

 diametric in such a way that, where the muscular contents 

 are divided into fibrils, each granule represents a part of a 

 fibril. The lateral disc is not very distinctly anisotropous ; 

 it is also not so elastic and not so closely connected with the 

 sarcolemma as the intermediate disc. 



" d. The isotropous band between the last-mentioned stripe 

 and the anisotropous transverse disc is always easily to be 

 recognised in the living fibre. Its thickness stands in a re- 

 verse proportion to that of the lateral disc. A two per cent, 

 saline solution, water, or very diluted spmt, causes at once 

 this isotropous band to turn dark. When heated up to 50° 

 Cent. (122° Fahr.) it becomes opaque and more firm, and 

 finally it shrinks. It is not a fluid substance, but consists of 

 a number of soft granules of equal size, which are so much 

 swollen that they touch each other completely ; the number 



