774 PROCEEDINGS OF SECTION J. . 
apply. and we can only conclude that a similar constitution, 
nervous and mental, has issued in like conduct. 
Insanity runs in families, and is transmissible by heredity. 
But it does not follow that an acquired character is trans-. 
mitted. The parent may bequeath his original tendency to 
insanity, which is developed by the child; and even then 
its appearance may be due, not only to the inherited pre- 
disposition, but also to surrounding circumstances. And 
it is not as if a definite kind of insanity, acquired by the 
parent, were transmitted to the child. In the offspring, the 
malady may take a form differing widely from a psycho- 
logical point of view, from that of the parent. It would 
rather seem that what is really transmitted is a nervous 
weakness, or instability, which may issue in one of many 
forms; and idiotcy or insanity may result from tuberculosis 
or epilepsy, as well as from defective intellect or imsanity 
in parents. We need not doubt that a lowered nervous and 
mental vitality, whether original or acquired, is transmis- 
sible to descendants; but this is a very different thing from 
a definite form of disease being stamped on the brain-cells 
and exhibited mentally, and then transmitted by heredity. 
On the subject of disease generally. the growth of medical 
opinion, as Dr. Jamieson remarks in a recent article, has 
been to minimise the importance of heredity. One reason 
for this is to be found in the germ theory, which has shown 
that illnesses are acquired through infection, in the lives 
of individuals, to a far larger extent than was formerly 
supposed. : 
The theory of use-inheritance has been employed to 
explain our knowledge of space, our conviction of the uni- 
versality of cause, and our moral intuitions. Let me briefly 
consider these as test-cases. 
At one time it was held by empiricists that our knowledge 
of space was derived, in the lifetime of each individual, from 
motor sensations. More recently, those who combine the 
theories of empiricism and evolution have thought that our 
idea of space is too great to be achieved in a single life, and 
that it is chiefly due to a succession of ancestral experiences. 
Thus, it has been held, the a@ priori and the a posteriori 
accounts of space may be reconciled, the knowledge of space 
being nativistic for the individual, though acquired in the 
experience of the race. The lion of empiricism and the 
lamb of a priori philosophy lie down together; but, as has 
been wittily remarked, the lamb lies down inside the lion. 
For the foundation of the theory is empirical. It is sup- 
posed that, at some remote time, motor sensations contained, 
