1904 - 5 .] Dr Aitken ok Evaporation of Musk. 901 
All the substances entered under natural and chemical products 
were samples of ordinary articles of commerce, and I am indebted 
to Sir John Murray for the piece of Kaizer Busuk from Christmas 
Island which was used in the tests. This Avood has a very 
strong and extremely offensive smell, strong enough and heavy 
enough to suggest solid particles ; yet it, like the others, only gives 
off gas or vapour. It may be interesting to sanitarians to know 
that sewage does not communicate to the air any solid particles, 
that the offensive emanation is a gas. As there seemed to be 
some doubt on this subject it was thought advisable to test it — 
though one would hardly expect solid or liquid particles to leave 
a wet surface. Further, it is known that the air in sewers is 
remarkably free from germs of all kinds, as they do not leave 
the sewage ; and if they are in the air they soon settle. If 
sewage gave off solid or liquid particles these also would soon 
settle on the surface of the sewage. These remarks apply only to 
sewers in which the sewage flows easily and without break in its 
surface film. If it is stirred up or flows rapidly, especially if 
over falls, then both germs and particles of the sewage get mixed 
up with the air, as the bursting of each bubble scatters a number 
of minute particles of sewage. 
Our nostrils seem to confirm the conclusion that the perfume 
given off by substances is not in the same form, and probably often 
not of the same composition, as the matter from which it is emitted. 
Take the effect of tobacco-snuff, for instance ; the perfume from 
it is perfectly distinct from the sensation produced when the dust 
of tobacco comes in contact with the nasal passages. The perfume 
is a soft and velvety sensation ; while the effect of the solid is 
sharp and biting, more allied to pain than pleasure. It may be 
said that this painful sensation is only the natural effect of over- 
stimulation of the nerves, just as the feeling of a fire is pleasant at 
a distance, while contact with the live coals is painful. The two 
sense perceptions are, however, so dissimilar it would be unsafe to 
draw too close a comparison. If they were similar, then an excess 
of all perfumes ought to be painful if the dust effect of the snuff 
were only an excess of perfume. But this is not the case. Musk, 
when snuffed, has hardly any effect, only the musky odour felt 
when no musk dust touched the nostrils. Other substances, such 
