720 PROCEEDINGS OF SECTION I. 
were, and are, in a manner, now considered under the 
headings of ‘extrinsic’? and “intrinsic.” But although 
this classification still suffices, a different importance is 
now attached to the parts that certain causes play: in the 
foundation and spread of maladies. Of the extrinsic 
causes, heredity stood foremost, occupying a far more 
important position in the opinion of experts, at that time, 
as a cause of disease, than it holds to-day. We recognise 
most thoroughly that nervous affections of all kinds, from 
insanity to a simple migraine, are transmissible, and what 
is more, neuroses are capable of being, as it were, culti- 
vated, intensified. or decreased, according as the parents 
are stable or otherwise in their nervous dispositions. We 
admit, too, that deformities and disfigurements, due to 
defective development, are passed down, though very 
uncertainly. In the transmission of nervous disorders, 
there is in a measure, a reliableness which is not found 
in handing down congenital defects. For instance, in the 
alcoholic, if the children are begotten whilst the parents - 
have given way to inebriate habits, the offspring are 
nearly always in some manner unsound in their mental 
organisation. 
Deformities, on the other hand, are rather what a 
horse breeder calls “failure, or the result of a nick.” 
Two perfectly healthy people, free from malformation 
of any description, marry, and their entire family may 
display evidences of imperfect development, such as 
auricular appendages, cleft palate, multiple fingers and 
toes, and so forth, from the eidest to the youngest child. 
Their offspring in turn may, and generally do, beget 
perfectly healthy children; but if the first-born is 
deformed, there is a strong probability that any others 
who may come into the world may be similarly affected. 
Deaf-mute may unite to deaf-mute, and their children be 
perfectly healthy. Now, it is not the same in mensal 
diseases. Nervous instability can be calculated almost — 
with certainty as to its transmissibleness. Formally, it 
used to be considered that the inter-marriage of relatives 
had much to do with the appearance of such irregularities 
as cleft palate, but this is considered to be very doubtful, 
and the evidence in its favour is far from strong. Hugg, 
a great authority on the subject, denies it altogether, and 
points in evidence to the intense relationship that 1aust 
have existed in the earliest and pre-historic stages of 
man’s being. Certainly, in all wild species, develop- 
mental aberrations are extremely rare, and, though tera*‘o- 
logical, are fairly common; the reverse being the case in 
