APPENDIX. 401 



of the pieces will probably be seen swimming about by means 

 of their cilia (Fig. 2). With these animal cells compare such 

 vegetable cells as pollen grains, spores of fungi, the cells com- 

 posing the bodies of some of the fresh-water algse, etc. 



As the satisfactory preparation of the tissues requires skill 

 obtained only by long training in manipulation and in the use 

 of hardening fluids, stains, etc., in many cases it will be prefer- 

 able to buy prepared specimens. These may be obtained at 

 slight expense from dealers in microscopic supplies. Such 

 specimens, as well as sections of various organs, are very neces- 

 sary, as it is only by a clear comprehension of the structure of 

 the difiEerent tissues and of the organs which they compose that 

 the student can understand the functions of the various parts. 



CHAPTER X. 



The principal chemical changes taking place during digestion 

 in the higher animals may be illustrated with very simple appa- 

 ratus, and at the cost of but little time. It is not necessary that 

 the student possess any knowledge of chemistry. The object 

 of digestion — viz., the changing of substances which are incapa- 

 ble of absorption into substances which may be absorbed, may 

 be made plain even to the youngest student. The chemicals 

 needed may be obtained of any druggist. 



The following experiments deal with the three principal di- 

 gestive fluids — viz., saliva, gastric juice, and pancreatic juice ; 

 and with the main kinds of foods — i. e., starchy, albuminous, 

 and fatty substances. 



Salivary Digestion. 



(l) The microscopical appearance of undigested starch and its 

 reaction with iodine. 



Into a test-tube about one-fourth full of water put a pinch of 

 corn-starch and shake the tube. Notice that the starch does 

 not dissolve. Examine a drop of the mixture under a micro- 

 scope and note the starch grains floating about in the water. 

 Add a drop or two of dilute iodine solution to the mixture in 

 the tube and note that it turns a deep blue. Examine a drop 



26 



