SCIENCE LETTER FROM PARIS. : 305 
ivory. It is to the sensibility of this pulp, that we immediately feel the least 
differences between heat and cold, and the slightest shades in the food masticated. 
The incisors have only a crown and a root, and constantly grow, as in the case 
of rabbits and other gnawing animals; they cut the food, while the canine teeth 
tear it. The ‘‘wisdom tooth” has roots and a crown less developed; its form 
varies, and it appears at no fixed age; when it has no room to develop, grave re- 
sults may ensue. When, through age, the teeth disappear, the form of the jaw 
bones alter, and impart a change to the physiognomy, the lower jaw bone in- 
clines backward, as with infants, and the chin becomes pointed. ‘Teeth grow ir- 
regularly from various causes, and the best period to correct the defect is be- 
tween ten and fifteen years of age. For persons who have acid stomachs, and 
which thus favor the destruction of the enamel, alkaline drinks ought to be pat- 
ronized, and alkaline powder, containing a little magnesia, employed. Caries 
can be either dry or humid—the former, often suddenly stops of its own accord, 
but commences by a black spot, and marked sensibility to heat and cold. When 
the disease eats into the pulp, the tooth ache appears in a most violent form. 
When caries appears, food should not be partaken of when too hot or too cold; 
brushes rather soft than hard, ought to be employed; alkaline powders are excel- 
lent for combating the acid of the saliva—one of the chief causes of caries—as 
stringent preparations fortify the gums. When the teeth are lost, they ought tor 
be replaced, not only in the interest of pronunciation, but in that of digestion, 
for on the efficacy of the latter a prolongation of our days depends. 
There are numerous thermal stations, spas in Europe: England has eight, Ger- 
many seventy-two and France 116. What is chiefly to be kept in view, is not 
the quantity of mineral matters in solution, but their quality. There is no classi- 
fication for natural mineral waters. Their production is one of the most inter- 
esting problems of geology; the mineralization is effected under the influence of 
heat and pressure; isin connection with the nature of the soil, and is associated 
with chemical reactions as complicated as they are obscure. ‘There is much dif. 
ference in composition of springs in point of yield, temperature and richness of 
solution, and they have a relationship with barometrical oscillations and earth- 
quakes. The Lisbon earthquake affected all the thermal springs of Europe. How- 
ever, the best known mineral waters have a very stable and ancient origin. 
THE SIXTH SENSE. 
| Dr. Hughes Bennett, Professor in Edinburgh University, lately read a paper 
_ before the British Association of Science, wherein he announced that the tendency 
of modern physiology was to ascribe to man asixth sense. If there be placed 
_ before a man two small tubes, the one of lead, the other of wood, both gilded 
_ over so as to look exactly alike, and both of the same temperature, not one of the 
five senses could tell the man which is lead and which is wood. He could tel 
this only by lifting them, and this sense of weight was likely to be recognized as 
the sixth sense.—Sczentific American. 
