QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 193 



which have been previously in close contact with each other ; 

 SO that all the discs of the muscular division must be regarded 

 as consisting in the living state of prismatic elements, which 

 are so swollen that they touch each other completely, and 

 which possess different chemical and physical properties in 

 the different discs, but the same properties in the same disc. 

 An intermediate fluid substance is not pre-existent, but is 

 pressed out by those elements when they coagulate. In a 

 second paper (ibid., vol. vii, part 2 and 3) Engelmann treats 

 of the changes of the individual discs of the muscular division 

 during contraction of the muscular fibres. For studying 

 these Engelmann uses, like Flogel, osmic acid. The living 

 muscular fibre is dipped into a solution containing 0*5 to 2 

 per cent, of this reagent for a few seconds ; it is then trans- 

 ferred into a half per cent, saline solution, which is afterwards 

 replaced by alcohol in a slightly rising concentration (50 to 

 90 per cent.), and is finally placed in turpentine. The con- 

 clusions which Engelmann draws fi*om his observations are 

 briefly these : 



*' a. The shortening force has its seat exclusively in the 

 anisotropous layer ; this latter thickens itself much more than 

 the isotropous. 



" b. The isotropous substance decreases, the anisotropous 

 increases in volume during contraction ; it must be therefore 

 assumed that fluid which is expressed by the isotropous is 

 imbibed by the anisotropous substance, viz. the latter swells, 

 the former shrinks, during contraction. 



" c. The isotropous substance becomes darker, more opaque, 

 the anisotropous brighter, more transparent, during contrac- 

 tion ; the median disc, however, does not become brighter. 

 From this it may be deduced that — 



" d. The isotropous substance becomes firmer, the aniso- 

 tropous softer, during contraction. 



" E. A. Sch'afer (* Proceedings of the Royal Society,' vol. 

 xxi) studied the structure of striped muscle on the muscular 

 fibres of the limbs of the common large water-beetle, mounted 

 without any reagent, and under high magnifying powers. 

 According to Schafer, every muscular fibre consists of a 

 homogeneous anisotropous ground-substance, in which are 

 imbedded dim cylindrical rods; these are isotropous, and 

 arranged in regular series. In the absolute state of rest the 

 muscular fibre presents, therefore, only the appearance of a 

 longitudinal fibrillation. In the normal state of slight ten- 

 sion the cylindrical rods change into rods with a swelling 

 at each extremity ; we have then muscle-rods consisting of a 

 shaft and two little knobs or heads. When this change has 



