70 MUSCULAR TISSUE. 



muscles of frogs, and in those of the tail of the rabbit, if quite 

 fresh. From these facts it is evident that the clear borders 

 of the proper substance need not be regarded as actually ana- 

 tomically distinct from the rest, but their presence can be ex- 

 plained as mere optical results of total rejection, i. e., provided 

 it be admitted that the interstitial substance and the proper 

 substance refract light in different degress. 



In order to study the lon'gitudinal striae preparations must 

 be made in humor aqueus of the fresh muscular tissue of 

 Hydrophilus, of the sartorius of the frog, or of the muscles 

 of the back of the lizard, care being taken to separate the 

 muscular bundles slightly from one another. In such propa- 

 gations it is seen that the substance which lies between two 

 [adjoining transverse striae appears to be marked off into a 

 number of quadrangular areas which correspond to the sides 

 lof the prismatic " sarcous elements." 



/ A number of such sarcous elements, arranged in a linear 

 series parallel to the axis of the muscle, and connected each 

 to each by shorter disks of transparent intermediary substance^ 

 together constitute a so-called primitive fibril. And, in ac- 

 cordance with this definition, we can conceive each muscular 

 fibre to be formed of primitive fibrils, along with the interme- 

 diary substance (corresponding to the longitudinal striae), by; 

 hich these fibrils are held together. It is no less possible to' 

 conceive of the muscular fibre as consisting of disks (each 

 composed of a number of laterally contiguous sarcous ele- 

 ments, along with the intermediary substance by which they 

 are, as just remarked, held together), separated each from 

 each by thinner disks of intermediary substance. The best 

 demonstration that the sarcous elements are the elements of 

 the muscular substance which are arranged in disks trans- 

 versely, and in fibrils longitudinally, is to be obtained by the 

 method of Cohnheim. A muscular fibre of a frog, Hyrophilus, 

 or cray fish is exposed in a platinum capsule to a freezing 

 mixture, at a temperature of 6 C. to 8 C. After a short 

 time the muscle acquires the consistence of wax. Fine sec- 

 tions are then made with the aid of a cooled razor, and are at 

 once examined in a drop of serum under a thin cover-glass, 

 care being taken to introduce slips of silver paper to avoid 

 pressure. Such a preparation, seen under Hartnack's immer- 

 sion objective No. 10, exhibits the following facts: Circular\ 

 /or oval disks present themselves (cross sections of muscular I 

 fibres), the margins of which are sharply defined and possess/ 

 la double contour (sarcolemma). Within the sarcolemma a 

 Beautiful mosaic is seen, in which the triangular, four-sided, or 

 pentagonal areas appear to consist of dull-looking material, 

 separated by lines which are brighter, more transparent, and 

 refract light less strongly. These linos are, in general, of 



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