PROBLEM 222 253 



it feels very warm. Now lightly touch all parts of the skin within 

 the square area. Do all parts feel the heat, or only the sense of 

 slight pressure of the nail? Mark with a little cross all spots 

 that are sensitive to heat. 



Now cool off the nail by placing it on ice. Wipe it dry and apply 

 while still cold in the same way to the area marked off on the 

 wrist. Do you feel the sensation of cold in all spots? Mark 

 as before, this time using a dot. 



NOTE. Certain sense cells of the body are sensitive to heat, others to cold. 



Conclusion. 1. Do these sense cells occupy the same area? 

 2. Do all parts of the skin feel heat and cold ? 



Problem 222 : To study the anatomy of the nervous system. 



Materials. Frogs preserved in formalin, with body cavity 

 opened and viscera removed, scissors, scalpels, forceps, hand lens, 

 charts showing nervous system of man, model of brain of man. 



Method. In a frog from which the organs of the body cavity 

 have been removed, note white glistening cords (nerves) which 

 seem to come from under the backbone. Follow the course of 

 some of the larger nerves. Where do they lead ? Now turn the 

 frog over and with sharp scissors and a scalpel remove very care- 

 fully the bony covering (the skull) from the whitish body (the 

 brain) . 



Observations. How many parts do there appear to be in the 

 brain? Notice the white elongated hemisphere of the fore brain 

 or cerebrum. The two anterior projections of the cerebrum are 

 called olfactory lobes. Where do these lobes seem to lead? 

 What do you think, from the name, their use is? 



Just back of the cerebrum, find two large lobes, known as optic 

 lobes, which have to do with sight. Look at the chart. Are 

 the eyes connected with the optic lobes? Back of the optic 

 lobe we find the cerebellum and medulla, the latter running directly 

 into the spinal cord, from which rise the spinal nerves you have 

 noted before. 



Compare, part by part, the brain of the frog with the model of 

 the brain of man. 



