THE FROG 99 



Vol. i, Figs. 3 and 4; or Marshall, The Frog, Fig. 7. Each 

 preparation should be framed by covering it with a plate of 

 glass of the same size as the cardboard (photographic nega- 

 tives cleaned by boiling or treating with nitric acid to re- 

 move the film are excellent for this purpose), supported by 

 strips of cardboard glued to the margins; the edges of the 

 glass and cardboard may then be bound together with passe- 

 partout, used in the same manner as for a lantern slide. The 

 permanency of such preparations will well repay the trouble 

 of making them. 



Some of the long bones (e. g., the humerus and the 

 femur) should be prepared by cutting, sawing or grinding 

 them lengthwise so as to exhibit a longitudinal half of the 

 bone with the interior cavity exposed. 



F. The Nervous System. Dissections of the central 

 nervous system made by a beginner are often unsatis- 

 factory, hence it is desirable that a supply of perfect prepara- 

 tions be provided. In particular see that the roots of the 

 cranial and spinal nerves are kept intact. For these prep- 

 arations choose large frogs which should be well hardened 

 in strong formalin (10 per cent.) before dissection is at- 

 tempted; it is well to remove the roof of the cranium in 

 order to admit the formalin. These preparations are best 

 kept in glass vials so that they may be viewed from all sides. 

 Permanent preparations showing the spinal nerves and the 

 sympathetic nervous system in situ are desirable. 



VI. HlSTOLOGICAL PREPARATIONS. 



For examination with the microscope, living tissues of the 

 frog should be mounted in normal salt solution, not in water, 

 since the latter causes plasmolysis. A physiologically nor- 



