BY DR. KLEIN. 71 



extreme tenuity, but certain spots are always to be observed, 

 within whi'.-h the areas of dulness are further apart ; in other 

 words, the clear lines of demarcation are wider. Wherever 

 this is the case there exist sharply defined nucleus-like bodies, 

 which, as we shall find, are actually the nuclei of the muscle- 

 corpuscles. In cross sections of muscular fibres of Crustacea, 

 insecta, amphibia, and reptilia, nuclei, surrounded by spots in 

 which the clear lines are thicker than elsewhere, are met with 

 in all parts of the fibres ; but in mammalia they occur only in 

 the immediate neighborhood of the sarcolemma. In the 

 Crustacea and in Hydroplrilus, the prevalent form of the 

 mosaic is pentagonal ; in the frog, four-cornered, and usually 

 rectangular. Provided that the preparation is protected from 

 pressure and evaporation, it remains unaltered for several 

 days. If a small quantity of water or very dilute acetic acid 

 is added to the fresh preparation, the disks swell out in a 

 remarkable manner; the polygonal areas become more trans- 

 parent and increase in size, while the intermediary substance 

 disappears. 



A fresh section, obtained as above, may be placed for a few 

 minutes in diluted serum and then transferred for from ten to 

 thirty seconds to half per cent, silver solution ; finally, washed 

 in water slightly acidulated with acetic acid, covered in glyce- 

 rin, and exposed to light. A preparation is thus obtained in 

 which the sectional disks are colored of various shades, from 

 clear j-ellowish-brown to dark-brown. Clear white lines on a 

 brown ground are seen with great distinctness, which corre- 

 spond completely with the trellis-work of transparent lines 

 seen in the fresh preparation, from which appearance we learn 

 that the spaces of the mosaic are stained brown by silver. 

 Oblique sections, whether examined fresh or after staining 

 with silver, exhibit corresponding appearances. In longitudi- 

 nal sections, prepared according to the same method, small 

 brown rectangles, longer in the direction of the axis of the 

 muscle than in the transverse direction, which correspond to 

 the sarcous elements, are here and there visible. These 

 rectangles are separated from each other by clear narrow lines. 



If a very small fragment of mammalian or frog muscle 

 (sartorius or mylohyoid of the frog, or the flat muscle in front 

 of the trachea of the rabbit), be steeped for fifteen or twenty 

 minutes in chloride of gold, then exposed to light for one or 

 two days in slightly acidulated water, and subsequently 

 hardened in common alcohol, sections can be made in planes 

 at right angles to the axis of the muscle. These exhibit 

 appearances which coincide in every respect with those above 

 described, the only difference being that the rectangular sar- 

 cous elements exhibit a clear red or purple tinge, while the 

 interstitial substance is dark. 



