PHYSIOLOGY. 191 



of the skull ; while the sheep's molars are cross-grooved, and 

 the jaw has a sliding articulation that permits the molars to 

 act opposite each other with a sort of millstone movement. 

 The human jaw is articulated so as to have all three move- 

 ments. What is the inference? It is said that a great 

 naturalist modelled from a single tooth a kind of animal that 

 he had never seen. 



The lungs of a small animal, a frog's for example, may be 

 inflated and dried ; they will retain the inflated form. The 

 viscera, brain and sense organs of small animals may be well 

 preserved, if kept from freezing, in sealed gem jars of water 

 containing three or four per cent, of formalin. Each time 

 before handling, the formalin should be well rinsed off as it 

 is injurious to living skin. 



Skeletons, or desirable parts thereof, may be prepared by 

 removing the skin, viscera, and most of the flesh and boiling 

 the remainder in water to which a small quantity of borax or 

 ammonia has been added. If necessary repeat the boiling until 

 in cold water all the bones may be cleaned off. Bones of 

 animals as small as a frog or mouse are glued or sewed in 

 proper position on cardboard. Wilder and Gage's soap may 

 be used for larger animals. To make this soap dissolve 5 oz. 

 ammonia, ^ to ^ oz. saltpetre, and 3 oz. white hard soap in 4 lbs. 

 of water. Boil the half -cleaned rat's or rabbit's skeleton for a 

 half- hour or longer in one part of this soap to four of water 

 and then for 20 to 30 min. in equal parts of the soap and 

 water. Clean by picking or brushing in repeated changes of 

 clear, cold water ; rinse and dry. The half-cleaned skeletons 

 may, instead of boiling, be buried for a few weeks in summer 

 near the surface of the earth, when decomposition, absorption, 

 and the action of worms will remove all the soft tissues. 



Physical and Chemical Experiments — To illustrate digestion 

 prepare an artificial stomach by dropping seven drops of 



