THE FROG 89 



the following reasons: (a) formalin specimens are unpleas- 

 ant to handle during dissection since the formalin vapor is 

 irritating to the eyes, and the solution may attack the fingers 

 causing severe poisoning of the skin; and (&) frogs pre- 

 served for a long time in formalin are almost worthless for 

 the preparation of skeletons, since the calcareous material 

 of the bones is gradually dissolved, leaving them soft and 



pliable. 



V. ANATOMICAL PREPARATIONS. 



It is frequently desirable that the student should see a' 

 model preparation of a system of organs as a guide for his 

 own dissection, or for the demonstration of features difficult 

 for a beginner to make out. Moreover, as in the case of the 

 skeleton, time and material will be saved by the use of per- 

 manent preparations that may be studied by successive 

 classes. At least one example of each of the preparations 

 described in this section should be provided. 



Wet preparations should be kept for exhibition in 5 per 

 cent, formalin or 70 per cent, alcohol; in some cases, which 

 will be pointed out, the alcohol has decided advantages. The 

 jars should be of clear glass, tall enough to permit of some 

 evaporation of the liquid before the preparation is exposed. 

 Glass tops, either clamped on over rubber rings or with edges 

 ground and made air tight by smearing with vaseline, are 

 desirable, since metal is attacked by formalin and cork will 

 discolor the alcohol. Each preparation should be provided 

 with an appropriate label. 



A. The Digestive System. An entire frog should be 

 prepared with the tongue protruded. This may be accom- 

 plished by injecting the lymph space beneath the tongue of 

 a fresh frog with warm gelatin prepared as follows : soak 



