VOLUNTARY MUSCLE. 115 



instance, thick enough for the purpose), and the 

 latter is then laid on, and the preparation examined 

 first with a low power, to make out the shape and 

 extent of the fibres, and afterwards very carefully 

 with an ordinary high power, and eventually with 

 as high a power as it is possible to obtain. In this 

 preparation almost all that is known of the struc- 

 ture of mammalian muscle may be made out the 

 delicate sarcolemma with the muscle nuclei imme- 

 diately beneath it, which look clear and oval when 

 the upper surface of a fibre is exactly focussed, fusi- 

 form when seen at the edge, the dark cross-stripes 

 of the muscular substance, seen by careful observa- 

 tion with a very high power to be pervaded by 

 parallel rod-shaped particles, the clear stripes bi- 

 sected by an intermediate dotted line, and finally a 

 longitudinal striation throughout the fibre, which 

 is the better seen in proportion as the transverse 

 striping is less marked. 



Preparation 4. For the purpose of bringing the 

 muscle-nuclei more distinctly into view, another 

 piece may be prepared in a drop of dilate acetic acid 

 (one part in 200 of water). The acid swells up and 

 softens the interstitial connective tissue, so that the 

 fibres are more readily separated the one from the 

 other, and it is found that, whereas in the former 

 preparation the muscle-nuclei could only be made 

 out by exercising the greatest care and attention, 

 they are now extremely obvious, studding the fibres 

 at intervals, but all of them quite at the surface of 

 the muscle under the sarcolemma. 



Preparation 5. When the frog's muscles are 

 prepared in like manner with acetic acid, the nuclei 

 are, on the contrary, seen to be embedded here and 

 there in the thickness of the fibre also. 



Preparation 6. The sarcolemma is extremely 

 delicate in mammalian muscle, and although it may 

 with care be made out even in the fresh preparation, 

 is nevertheless much more easily demonstrated in 

 the muscles of the lower vertebrata, the fro^, for 



