28 Animal Micrology 



PRACTICAL EXERCISE 



Kill a frog by placing it under a bell jar which contains a bit 

 of cotton saturated with chloroform. Open the body as soon as 

 possible after death and secure the tissues specified below. 



1. Alcohol Fixation. Remove the dorsal aorta and small 

 pieces of the liver and harden in absolute alcohol (at least, not 

 less than 95 per cent.) in a vial or small bottle. The tissue will 

 be ready for further treatment in two days. 



Larger pieces of tissue require longer time. The pieces should 

 be thin. Change the alcohol every day for the first three days. 



Alcohol is in many instances an unsatisfactory fixing reagent, 

 but it is frequently employed because it is usually at hand and is 

 easily manipulated. Hot absolute alcohol is very often used for 

 insects. If absolute alcohol is used, the fixation may be fairly 

 good, but because of the expense attached to the best absolute 

 alcohol, the lower percentages are more frequently used. They 

 shrink protoplasm, however, and are not to be recommended for 

 the finer histological work. Ninety-five per cent, alcohol is as 

 low as should be used for fixing, although 70 per cent, is sufficient 

 to preserve specimens for other than microscopical work. Acetic 

 acid (Appendix B, 2) is used with alcohol sometimes to increase 

 penetration and to counteract its tendency to shrink tissues. The 

 mixture is usually preferable to alcohol alone. 



2. Fixing with Gilson's Mercuro-Nitric Mixture. Place small 

 pieces of liver, kidney, pancreas, esophagus, cardiac and pylo- 

 ric ends of the stomach, apex of the heart, bladder, testis or 

 ovary, and tongue in Gilson for from two to six hours. Remove 

 a piece of intestine about 12 mm. long, and after washing it 

 thoroughly in normal saline place it in a small vial containing 

 about fifty times its bulk of fixing mixture and leave it for two 

 hours. After fixation wash the objects thoroughly in water fol- 

 lowed by 35 and 50 per cent, alcohol (15 minutes each), and pre- 

 serve them in 70 per cent, alcohol. Read remarks on washing 

 out corrosive sublimate, Appendix B, reagent 13, caution 1. 



Gilson's is an excellent general reagent and gives a very deli- 

 cate fixation. It is perhaps the most satisfactory killing and fix- 



