INTRODUCTION. 1X 
distinguished French chemist, to a minute trace of a camphorated 
body the exact constitution of which has not yet been determined. 
It is so odorous that even a trillionth of a milligramme gives a 
perceptible smell. 
It may seem surprising that the delicate organs of the sense of 
smell should remain unimpaired over a number of years and 
uninjured by thoughtless and careless usage, but, as a matter of 
fact, they do suffer in acuteness by such causes, although not to 
such an extent as the organs of sight. 
The sense of smell is not equally developed in mankind ; on 
the average it is much more delicate in males than in females, but 
the degree of keenness ranges widely as between individuals ; thus, 
in an experiment on record, three male observers were able to 
detect 1 part of prussic acid in 2 million parts of water, though in 
this proportion its presence was not revealable by a chemical test ; 
others, of both sexes, could not detect prussic acid in solutions of 
almost overpowering strength. 
Few people have perfect sight, the focal range of one eye generally 
differing from that of the other ; many people are conscious of this 
defect, and to balance the inconvenience wear a glass in one eye ; 
many are unconsciously partially colour-blind (some totally so, 
as proved by recorded examinations of men, applying for work as 
engine-drivers, not being able to distinguish between red and 
green) ; also very many are unconsciously deficient as regards their 
olfactory sense and the sense of taste which is dependent upon it. 
On placing a sapid substance in the mouth and at the same time 
closing the nostrils, the sensation of taste is suspended, conse- 
quently persons with an imperfect sense of smell have also an 
imperfect sense of taste. Some substances have a strong taste 
without any or without much scent. Odour which accompanies 
taste is termed flavour. Flavour has been defined as an inter- 
mediate sensation between taste and smell. 
Some races, such as Ethiopians and North-American Indians, 
are remarkable for the acuteness of their sense of smell, ac- 
counting for their wonderful power in tracking enemies. This 
