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 algae, etc. 
As the satisfactory preparation of the tissues requires shill 
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 different 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. 
(1) 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 
