126 PROGKESS OF mCROSCOPIOAL SCIENCE. 



disk, the rods of which have become shorter ; they are reduced to two- 

 thirds of their original length in the centre of the wave. 



To preserve preparations, Flogel recommends the following me- 

 thod. The whole Trombidium having been kept for one or two hours 

 in a solution of 1 per cent, perosmic acid, is placed in diluted alcohol, 

 which in the coui-se of several weeks is gradually replaced by strong 

 alcohol. After this, the object is transferred into turpentine, and is 

 finally dissected in solution of Canada balsam. 



Dr. Merkel writes on the striped muscle in Max Schultze's 

 ' Archiv,' vol. viii., part 2. He uses for his investigations the muscles 

 of the thorax of the fly and the bee, either in the fresh condition after 

 rigor mortis has appeared, or oftener after hardening with alcohol of 

 60 or 100 per cent. 



Each muscular fibre appears to be divided into a nimiber of trans- 

 verse divisions, each of which is bounded at its extremities by a 

 terminal membrane closely united with the sarcolemma. Through the 

 middle of each division a membrane stretches transversely across ; 

 this corresponds to the median disk of Hensen, and is also fixed to the 

 sarcolemma. The terminal membranes of two adjacent divisions are 

 united by a thin intermediate substance, so as to form apparently one 

 (lisk — the terminal disk of Merkel. These parts represent, so to 

 speak, the framework of the muscular divisions. Each of the divisions 

 is filled with transparent fluid substance, in which lies accumulated, 

 at the sides of the median membrane, the gelatinous contractile sub- 

 stance, the proper transverse stripe ; it falls away gradually towards 

 the terminal disk. In the state of contraction, a remarkable difference 

 in the appearances just stated is to be noticed ; the terminal disk 

 becomes thinner, the contractile substance leaves its former place at 

 median membrane, having accumulated close to the terminal disk ; 

 consequently, each muscular division contains now one half of the 

 contractile substance at each of its extremities. In the state of con- 

 traction, the contractile substance is darker than in the state of rest. 



When a muscular fibre contracts, the individual divisions do not 

 pass at once from the state of rest into that of contraction, but they 

 go first through an intermediate state. This latter is characterized 

 by the disappearance of all optical differences, the contents of the 

 muscular division being perfectly homogeneous and at the same time 

 very bright. This intermediate state represents, according to Merkel, 

 the clue for explaining the above-stated displacement of the contrac- 

 tile substance ; for during the intermediate state the contractile sub- 

 stance, imbibing all the fluid that is contained in the division, swells 

 so as to fill out this completely, and, having gone through this pre- 

 paratory state, again presses out this fluid, and accumulates on both 

 ends of the division beside the terminal disk. The individual par- 

 ticles of the contractile substance press as close as possible to the 

 terminal disk, the former trying to come into contact with the latter by 

 as many of its particles as possible ; in consequence of which the 

 muscular fibre not only becomes broader, but also the fluid which is 

 pressed out by the contractile substance is now accumulated in the 

 middle of the division at the sides of the median membrane. As far 



