192 QUARTERLY CHRONICLE OV MICROSCOPICAL SCIENCE. 



of these particles corresponds to the number of fibrils into 

 which the muscular contents split up occasionally. 



" e. In the fresh living muscular fibre the dim broad trans- 

 verse disc appears to be divided into two by a median bright 

 homogeneous transverse band. In some cases, however, the 

 latter is not to be made out as a separate structure. Between 

 crossed Nicol's prisms, both the transverse discs and the 

 median disc are seen to be anisotropous. If fresh living 

 muscular fibres' be treated with a 5 per cent, saline solution, 

 the transverse discs become swollen and pale, whereas the 

 median disc becomes darker and narrower. Diluted acids 

 and alcohol of 25 to 60 per cent, have a similar action. 

 Heating brings out the median disc and the transverse discs 

 also, as different structiires. 



" When a muscular fibre dies spontaneously, or is subjected 

 to the influence of water, diluted chromic acid, alcohol, cor- 

 rosive sublimate, &c., the anisotropous substance appears to 

 be composed of highly refractive anisotropous rod-like bodies 

 — sarcous elements, muscle-rods — and of a less refractive 

 isotropous amorphous intermediate substance. Engelmann 

 distinctly denies that these elements are distinguishable in 

 the muscular fibre while in a living condition ; for those 

 parts, in which these elements have made their appearance 

 are without exception non irritable. 



" In some cases the anisotropous discs are the only parts 

 of the muscular divisions which have split into rods, the other 

 parts not showing any sign of a longitudinal difi'erentiation ; 

 e. g. in muscular fibres of insects which have died spon- 

 taneously or which have been treated with water, very diluted 

 saline solution, or diluted alcohol. In most cases, however, 

 especially in locustida amongst insects, and in vertebrate ani- 

 mals in general, the disintegration takes place through all the 

 discs of the individual divisions ; in this way the so-called 

 primitive fibrils make their appearance. On observing the 

 optical longitudinal section of a fresh muscular fibre for some 

 time the discs of the divisions, at first absolutely homogeneous, 

 show immeasurably fine j)ale isotropous longitudinal lines ; 

 they are in most regular distances from each other, not more 

 than 0*001 of a millimetre. These lines gradually become 

 brighter, and at the same time broader — their thickness 

 exceeding the O'OOOoth part of a millimetre — at the expense 

 of those parts that lie between them, without the muscular 

 fibre, as a whole, altering in diameter. Consequently it may 

 be said that the appearance of the longitudinal bright line is 

 caused, not by the SAvelling of a pre-existent intermediate 

 substance, but by the shrinking, i. e. coagulation, of elements. 



