3 8 PRACTICAL HISTOLOGY. 



INTRA-NUCLEAR PLEXUS OF FIBRILS IN NON-STRIPED MUSCLE. 

 The student who desires to show this arrangement must proceed as follows : 



PREPARATION. Kill a newt and place the small intestine and mesentery in a five per 

 cent, solution of ammonium chromate for twenty-four hours. Wash in water till no colour is 

 given off, then transfer it to picrocarmine for several hours. With scissors snip off a small 

 piece of the mesentery and mount it in glycerine. Cover. 



EXAMINATION (H). Observe the very large spindle-cells, either single or disposed in 

 groups. Study a nucleus and observe in its interior a delicate plexus of fibrils. In its in- 

 terstices lies a clear homogeneous substance. On carefully focussing with one-eighth of an 

 inch objective, fibrils may be traced through the poles of the nucleus, and be found to be con- 

 tinuous with fibrils disposed in the long axis of the cell. These muscular fibres are examined 

 on account of their large size (Klein). (Indicate tliese plexuses of fibrils in PI. VII., Fig. 5.) 



MESENTERY OF NEWT DOUBLY-STAINED WITH PICROCARMINE AND LOGWOOD. 



PREPARATION. Prepare the mesentery of a newt with ammonic chromate as directed 

 above. After washing away all the chromate from a piece of the mesentery, stain it for 

 fifteen minutes in dilute picrocarmine (ten drops to a watch-glass of water). Wash it 

 in water and place it in water acidulated, with a few drops of acetic or picric acid 

 for an hour. After washing place it in dilute logwood solution, until it assumes a faint lilac 

 colour, taking care that it is not over-stained. Mount it in glycerine. 



STRIPED MUSCLE. 



This may be studied in any of the voluntary muscles. A muscle consists of striped muscu- 

 lar fibres held together by connective tissue and supplied with blood-vessels and nerves. The 

 fibres must be examined in the fresh condition, and after the action of reagents. 



FRESH STRIPED MUSCLE. 



PREPARATION. Kill a frog, and from one of its muscles preferably the sartorius, because 

 it is composed of parallel fibres snip off a small piece and tease it slightly in salt solution. 

 Cover. 



EXAMINATION (H). Observe the cylindrical fibres consisting of the sarcous substance 

 marked with alternate light and dim stripes (PI. VII., Fig. 8). In some places the striation 

 may be obscure or the stripes very close, while here and there slight longitudinal fibrillation 

 is observable. Irrigate with distilled water and after a short time a fine bleb may be seen on 

 the side of one or more of the fibres. This is the sarcolemma. (Indicate the sarcolemma in 

 PI. VII., Fig. 6.) Water has passed through the sarcolemma and raised it from the sarcous 

 substance. Irrigate the preparation with dilute acetic acid, when the nuclei, lying under 

 the sarcolemma and in the sarcous substance, are revealed (PI. VII., Fig. 7). They are 

 elongated spindles, sometimes slightly coloured, lying in the long axis of the fibres. The 

 reason why the nuclei are not seen at first is because they have the same refractive index as 



