INTRODUCTION. 27 



c.c. + 5% potassium bichromate, 500 c.c.) one week 

 in the dark. Light causes a precipitate. At the end 

 of one week the specimen should be placed in 1000 

 c.c. of 5% formalin for another week, after which it is 

 ready for dissection. In case brains of calves or sheep 

 are used a hammer and bone chisel are necessary for 

 opening the skull. The head should first be nailed to the 

 tray. As soon as the brain is removed it should be 

 placed in a large pan of water and the dura mater care- 

 fully cut away, the clotted blood washed off and a 

 syringeful of strong formal-bichromate injected into the 

 third ventricle by pushing the cannula about half an 

 inch through the infundibulum (Fig. 94). The brain 

 of a sheep or calf will be very soft when removed, as it 

 cannot be hardened previously by injecting the harden- 

 ing fluid into the arteries. Therefore it is necessary 

 to lay the specimen on absorbent cotton in the jar 

 of formal-bichromate, which must be exchanged for 

 fresh fluid on the second and third days. At least two 

 weeks are required for hardening the brain of a sheep or 

 calf, after which it is placed in 5 r ( ' formalin for a week 

 or more to wash out the bichromate before dissection. 

 Brains are best preserved permanently in 85 c [ alcohol. 



Preparation of the Osseous System. A mounted skele- 

 ton of the cat may be purchased for about eight dollars. 

 A partially articulated skeleton may be easily prepared in 

 the laboratory by cutting most of the flesh from a speci- 

 men soaked in formalin two weeks. After drying a few 

 days the remaining tissue is easily removed from the 

 bones, which will remain articulated if the ligaments at 

 the joints are not cut. Clean disarticulated bones are 

 best secured by following directions given in the " Ana- 

 tomical Technology " bv Wilder and Ga^e. A beautifully 



O _/ _/ O J 



cleaned set of bones may also be obtained by exposing 

 to the weather during the summer the skinned carcass. 



