al examination and recorded statistics that the use
of tobacco among college students checks growth in weight, height,
chest-girth, and, most of all, in lung capacity.

Additional Experiments.

Experiment 66. Test a portion of _C_ (Experiment 57) with solution
of iodine; no blue color is obtained, as all the starch has disappeared,
having been converted into a reducing sugar, or maltose.

Experiment 67. Make a thick starch paste; place some in test tubes,
labeled _A_ and _B_. Keep _A_ for comparison, and to _B_ add saliva, and
expose both to about 104 degrees F. _A_ is unaffected, while _B_ soon
becomes fluid--within two minutes--and loses its opalescence; this
liquefaction is a process quite antecedent to the saccharifying process
which follows.

Experiment 68. _To show the action of gastric juice on milk_. Mix two
teaspoonfuls of fresh milk in a test tube with a few drops of neutral
artificial gastric juice;[30] keep at about 100 degrees F. In a short
time the milk curdles, so that the tube can be inverted without the curd
falling out. By and by _whey_ is squeezed out of the clot. The curdling
of milk by the rennet ferment present in the gastric juice, is quite
different from that produced by the "souring of milk," or by the
precipitation of caseinogen by acids. Here the casein (carrying with it
most of the fats) is precipitated in a neutral fluid.

Experiment 69. To the test tube in the preceding experiment, add two
teaspoonfuls of dilute hydrochloric acid, and keep at 100 degrees F. for
two hours. The pepsin in the presence of the acid digests the casein,
gradually dissolving it, forming a straw-colored fluid containing
peptones. The peptonized milk has a peculiar odor and bitter taste.

Experiment 70. _To show the action of rennet on milk_. Place milk in a
test tube, add a drop or two of commercial rennet, and place the tube in
a water-bath at about 100 degrees F. The milk becomes solid in a few
minutes, forming a _curd_, and by and by the curd of casein contracts,
and presses out a fluid,--the _whey_.

Experiment 71. Repeat the experiment, but previously boil the rennet. No
such result is obtained as in the preceding experiment, because the
rennet ferment is destroyed by heat.

Experiment 72. _To show the effect of the pancreatic ferment (trypsin)
upon albuminous matter_. Half fill three test tubes, _A, B, C_, with
one-per-cent solutio