mTEODTJCTION XIX 



tions, and it consists almost entirely in the removal of the 

 connective tissues which bind the different organs together. 

 The student must plainly understand that hacking specimens 

 to pieces is not dissection. 



While dissecting, the following rules should be borne in 

 mind ; 



1. Fix the specimen in whatever position may be most 

 convenient for work. If it be a large object, as, for exam- 

 ple, a lobster or frog, lay it dorsal or ventral side uppermost • 

 as may be desired, and with the head turned away from one. 

 If the specimen be so easily moved as to interfere with the 

 work, stick pins obliquely through the softer tissues into the 

 dissecting- tray or the wax in the bottom of the dissecting-pan. 



2. The tissues of fresh specimens must be moistened from 

 time to time with water or with noritial salt-solution to pre- 

 vent the drying and distortion of parts. Alcoholic material 

 should be examined in dishes containing fifty per cent, alco- 

 hol. If such specimens be large, e. g., lobster, and it be de- 

 sirable to examine them on the dissecting-tray, place them 

 for two or three hours previous to the time when wanted in 

 a mixture of equal parts of water, alcohol, and glycerine. 

 They will then keep moist even in the open air. 



3. Before making a cut in any direction, study the speci- 

 men carefully, and note where the cut must be made in or- 

 der to expose the part wanted with the least injury to sur- 

 rounding parts. Specimens unnecessarily mutilated should 

 be replaced at the expense of the student. 



4. In dissecting and cleaning muscles, nerves, and blood- 

 vessels, stretch them slightly and work in the direction of 

 their length, never crosswise. 



5. Avoid unnecessary handling of the parts, and do not 

 pinch them with the forceps. 



6. Do not allow scraps to accumulate on the specimen. 

 Sponge away blood-clots. With a pipette wash away the 

 debris which accumulates on specimens dissected under wa- 

 ter, or change the water frequently. 



