224 APPENDIX. 



and low melting-points, should be mixed in such proportions that 

 the melting-point lies between 50 and 55 C. 



Perenyi's Fluid. Ten-per-cent nitric acid 4 parts, 90# alco- 

 hol 3 parts, # aqueous solution of chromic acid 3 parts. Not 

 to be used until the mixture assumes a violet hue. Leave objects 

 in the fluid 30 minutes to an hour, then 24 hours in 70# alcohol, 

 and finally place in 90 per cent alcohol. 



Schultze's Macerating Fluid. Dissolve a gram of potassium 

 chlorate in 50 c.c. of nitric acid. The tissue should be boiled 

 in the mixture and afterwards thoroughly washed in water. 



Schulze's Solution. Dissolve zinc in pure hydrochloric acid, 

 evaporate in the presence of metallic zinc, on a water-bath, to a 

 syrupy consistency, add as much iodide of potassium as will dis- 

 solve, and then saturate with iodine. (When heated with this 

 fluid cellulose turns blue. 



Section-cutting. Many objects can be cut by hand with a 

 razor (which must be very sharp). The object should be held in 

 the left hand while the razor is pointed away from the body, and 

 allowed to rest on the tips of the fingers with its edge turned 

 towards the left. It is then drawn gently towards the body so 

 as gradually to shave off the section. Small objects may be held 

 between two pieces of watchmaker's pith previously soaked in 

 water. In either case the razor should be kept wet. 



Many objects, however, require more careful treatment by 

 one of the following methods : 



A. Paraffin Method. After hardening and staining, the 

 object is soaked in strong alcohol (95$ or more) until the water 

 is thoroughly extracted (2-12 hours, changing the alcohol at 

 least once), then in chloroform until the alcohol is extracted 

 (2-12) hours), and then in melted paraffin (not warmer than 55 

 C.) on a water-bath for 15 to 30 minutes (too high a tempera- 

 ture or too long a bath causes excessive shrinkage). Some of the 

 paraffin is then poured into a small paper-box, or into adjustable 

 metal frames. The object is transferred to it and after the mass 

 has begun to set it is placed in cold water until quite hard. It 

 is then cemented (by paraffin) to a square piece of cork and 

 placed in the section-cutter or microtome. 



The sections may be cut singly with the oblique knife or by 



