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POPULAR SCIENCE REVIEW. 
most extensive and celebrated establishments, is the choosing of the mate- 
rials. These are felspar, silica, and clay. To these are addefc various 
metallic oxides to produce any shade of colour desired. The felspar, clay, 
&c., are ground to an impalpable powder under water, dried, and made into 
a paste. That composing the body of the tooth is of different materials 
from that composing the base or enamel. The teeth are made in brass 
moulds, and this is quite a delicate process. The enamel is first put in 
place with a small steel spatula ; the platinum rivets, by which the teeth 
are fastened to the plate, are placed in position, and then the body is pressed 
into the mould. They are then submitted to powerful pressure and dried. 
After being dried, they are submitted to a process called biscuiting, in 
which they can be cut like chalk. They are then sent to the trimmers, 
who scrape off all proj ections, and fill up all depressions which may have been 
left in the operation of moulding, and then wash them with what is techni- 
cally termed enamel. This is composed of various substances, more fusible 
than the tooth itself, and answers the glaze in common porcelain making. 
It is ground to a fine powder, and suspended in water, and is laid on with a 
camel-hair brush. They are now sent to the gummers, who apply the 
gum. This is chiefly composed of oxide of gold, and is applied in the same 
manner as the enamel. After being dried, they are burned. This operation 
is carried on in a muffle. The teeth are placed on a bed of crushed quartz, 
which is placed on a slab of refractory clay. After being exposed to an 
intense heat for some hours, they are taken out, cooled, and assorted.” 
The New (?) Ancesthetic. — It has been stated in various medical and 
scientific journals that Dr. Liebreich has discovered a new anaesthetic — 
Chloride of Ethylene. In point of fact, we believe that this is no new 
discovery ; for this substance was employed even by Dr. Snow in some of 
his inquiries. Its merits too appear to have been much overrated. 
A Neiv Theory of Nervous Sensation. — The Chemical News (June 3) 
gives a report of a recent meeting, of the Royal Irish Academy at which a 
paper was read by Dr. Robert M‘Donnell on the above subject. The 
author’s paper might be briefly described as an application of a theory 
similar to the wave theory of light to the propagation of sensation along the 
nerves. He compared this 11 undulatory ” theory of nervous conduction 
with the hitherto more generally received hypothesis of distinct nerve- 
conductors, supposed to exist for each kind of sensation, pain, heat, tickling, 
&c. ; and attempted to point out that the former is at once a simple hypo- 
thesis, and more in harmony with the ideas now prevalent as to the propa- 
gation of light, heat, electricity, &c. The author also dwelt upon many 
points of analogy between the absorption or interception of waves of heat 
or of light, and the somewhat similar phenomena as regards nerve-conduc- 
tion where one kind of sensation is felt and another ceases to be any longer 
perceived, as in cases where the patient feels the contact of the hand, but 
cannot distinguish heat, or vice vcrsd. 
Action of Alcohol on the Body. — A paper was read before the Royal 
Society in May by Professor Parkes and the Count Wollowicz, M.D., 
detailing their experiments on the action of ordinary alcohol on the human 
body. Among the results were the following : — Small quantities of abso- 
lute alcohol (1 and 2 fluid ounces = respectively to 28-4 and 56*8 c.c.), given 
