LABORATORY EXERCISES 417 



specially devised chamber. It is not a practical experiment to attempt 

 with limited time and apparatus. 



Page 282. To try out the point that heart muscle is apparently not 

 susceptible of tetanus, lay bare the heart of a frog of which the brain is 

 destroyed, and bend the electrodes of such an apparatus as is shown on 

 opposite page so that the heart may be placed between them. Rapid 

 making and breaking of the current can then be secured by use of the key. 



CHAPTER XVIII 



Page 290. The bones of the head of a cat are sufficiently thin so 

 that they dissect easily. The brain coverings, fluids present, main divi- 

 sions of the brain, and distribution of blood vessels can be admirably 

 shown in such a dissection. If it is desired to show the distribution of 

 gray and white matter, take such a brain (or preferably that of a sheep) 

 and wrap it in cotton to prevent flattening against side of jar, and place 

 for two weeks or so in potassium bichromate solution (see Formula 10). 

 Sections can then be made through it with a razor and internal structures 

 shown to any desired extent. The brain can be hardened immediately 

 in formalin (5%), but will not show above differentiation. 



While the brains of fishes have their parts developed to sizes which differ 

 from those of the cat's brain, their general relations and order of arrange- 

 ment are the same. The cartilage skull of the shore dogfish (Mustelus or 

 Squalus) permits very easy and beautiful demonstration of all brain parts 

 and nerves. See address list of dealers. 



Page 293. In order to demonstrate the so-called gray and white 

 regions of the central nervous system, the parts must be prepared in spe- 

 cific ways. See formula for this purpose. Even free-hand sections of such 

 material make clear demonstrations. 



Page 294. Prepared sections of the cortex of the brain show cells 

 well, though the student will get but a limited idea of the brain as a whole 

 from any one section which may be studied. 



Page 301. The general appearance and structure of the spinal cord 

 can be well learned by obtaining at a market a piece of the spinal cord of 

 some animal (e.g. the sheep or ox) still in its coverings. If this is hardened 

 in equal parts of 5% formalin and 70% alcohol, it is easily handled. If the 

 potassium bichromate method is followed the results will be better yet. 



Prepared sections of the spinal cord will also be interesting. 



Page 302. That the cord is the path through which nerve impulses 

 are sent out from the brain can be shown on the body of a freshly beheaded 



