PROBLEM 184 221 



be expert physiological chemists. But we can obtain and understand some of the 

 data involved. It is with such an end in view that the rather curtailed lists of 

 important happenings in the process are here outlined. 



Problem 184t' To compare the digestive system of a frog with 

 that of man. 



Materials. — Opened frogs preserved in 4 per cent formalin, 

 manikin showing digestive tract, opened frogs' stomachs, hand 

 microscopes, charts of digestive systems or diagrams on page 297, 

 Civic Biology. 



Method and Observations. — Note in the opened specimen 

 of the frog the glistening membrane {peritoneum) lining the body 

 cavity. It is this membrane in man that becomes inflamed and 

 causes peritonitis. 



Notice the large, reddish brown organ covering most of the other 

 organs. This is the liver. Count the lobes or divisions of the liver 

 and compare the position and general structure with the liver 

 of man (use manikin). Lift up the middle lobe of the liver and 

 find the gall bladder, a greenish sac. This contains bile, a secre- 

 tion from the liver. Now compare with the manikin to see if you 

 can locate where the bile gets into the food tube. 



The food tube begins at the mouth, continues as a short wide 

 gullet into the stomach (just under the liver). Compare these 

 structures in the frog with similar structures in man. The stom- 

 ach of the frog leads into a long coiled small intestine and thence 

 into a very short large intestine. What difference is there between 

 the frog and man in this respect ? Note that all the organs are held 

 in place by a fold of the body cavity lining called the mesentery. 

 What might its use be? A pinkish body, the pancreas, can be 

 located between the stomach and the first bend of the small 

 intestine. 



Look at the open stomach ; notice the folds and ridges on the 

 inner wall and determine which way they run. 



Look at a mounted section of the small intestine of a dog or a 

 cat through a compound microscope to note the small elevations 

 of its inner lining called villi. Would these projections give more 

 surface to the small intestine? 



Conclusion. — 1. Compare, part for part, the digestive tract 



