Natural History. 393 
then the air, which becomes more or less charged with the odorous 
particles which a sapid and odoriferous substance in the mouth has 
emitted not being able to pass by the nose, cannot any longer carry 
those particles to the membrane which occasion the sensation of smell. 
When therefore the nostrils are pressed together, no other sensations 
are perceived than the taste and the touch of the tongue. One can 
hardly form an idea of the extreme difference which exists between 
the sensations produced by a sapid and odorous substance in the 
mouth according as the passage of the air expired by the nose is 
open or interrupted. 
I have ultimately established four classes of bodies relative to the 
sensations which they excite when put into the mouth, amongst 
which I do not include those caustic substances which attack and 
alter the organs. 
Ist Class. Bodies which act on the tongue only by touch.—Rock- 
crystal, sapphire, and ice. 
2d Class. Bodies which act by »y touch on the tongue and by smell.— 
The odorous.metals: when tin is put into the mouth the odour of 
that metal is perceived; but on pressing the nostrils all sensation, ex- 
cept that of touch only, entirely disappears, 
3d Class. Bodies which act by touch on the tongue and by tasteom— 
Such bodies as these are sugar, salt, &c. When these substances 
are put into the mouth the sensations they cause are not modified by 
pressing the nostrils together. 
Ath Class. Bodies which act by touch on the tongue, and by taste 
and smell, Examples 1. Volatile Oils.—They are generally acrid, 
but with a particular odour for each sort of oil. When put into the 
mouth, and the nostrils are pressed, the acrid gemsation: is always 
sensible, whilst that of smell vanishes entirely. 2. Lozenges of Pep- 
permint, Chocolate, &c.—When the nostrils are saa “after these 
have been introduced into the mouth, nothing is perceived but the 
savour of the sugar ; but if the nostrils be relieved, the odour of the 
peppermint or the chocolate becomes evident. 
It will not be useless to remark that the urinous taste attributed to 
fixed alkaline bases, does not belong to these substances, but to the 
ammonia, which is set at liberty by their action on the ammoniacal 
salts contained in the saliva. ‘The proofs of this are the disappear- 
ance of the sensation referred to, when the nostrils are pressed, and 
the perception of the same sensation when one smells to a mixture of 
recent saliva and alkali, made in a small glass or porcelain capsule. | 
It appears that the sense of smell weakens by age, before that of 
taste.—Mem. du Mus. x. 439, 
2. Action of Meconic Acid on the Animal Economy.—Doubts hav- 
ing arisen with regard to the effects produced by pure meconic acid 
and the meconiates on the animal system, i Signori Fenoglio, Cesare, 
