5. Discuss relation of high temperature to health.
6. Why are burns of so much importance as a problem of defensive hygiene?
7. Discuss relation of insufficient sunlight to rickets?

8. What defensive hygiene measures are particularly indicated in the
University to meet the hazards of insufficient light?

XIV. DEFENSIVE HYGIENE OF HEREDITY

Our knowledge of heredity has been transferred from the realm of spec-
ulation to the realm of experiment. The rediscovery in 1900 of the work
of Mendel furnished the foundation for the rapid growth of the science
of genetics,

Normality and Abnormality

As a result of the statistical and experimental study of heredity,
we have had revealed to us with great vividness the mechanisms by which
‘both normal and abnormal characters can be transmitted from generation
to generation. The knowledge of these mechanisms has uncovered for us
some of the most pressing problems of Defensive Hygiene.

Problems

The principal problems of heredity for which we should adopt a more
intelligent and agressive defensive program are:

(a) Hereditary mental diseases
(vo) Feeblemindedness
(c) Nervous and mental instability.

Extent of Problem

While there is some controversy over whether the large increase in
mental deficiencies of various kinds is an absolute or relative one, there
is no doubt of the immensity and importance of the problem. An intelli-~
gent opinion upon control measures should be based upon a working know-
ledge of the basic and exciting causes of:

(a) Mental diseases
(b) Feeblemindedness.

Control of Human Heredity

Even though we have accumulated considerable knowledge of the mechan-
isms of both normal and abnormal heredity, it is a difficult and complex
problem to apply in the human field.

Any program of applied eugenics to be successful must be practical
and not visionary. In this course we are concerned directly with the pre-
vention side and only indirectly with the constructive side.