Bauhaus-Universität Weimar

120 
THE CRYSTALLINE LENS. 
increased size of the jaw-bones, the formation of new teeth becomes 
necessary. The permanent teeth begin to appear about the sixth or 
seventh year, but -their crowns are formed at a very early period. 
Of the twenty temporary or milk-teeth, eight only are molares; the 
permanent teeth are thirty-two in number, and of these twenty are 
molares, or twelve true molares, and eight bicuspides. 
The dental substance of the first great molaris of the second set 
begins to be deposited towards the end of pregnancy. The sockets 
of the new teeth are gradually separated from those of the old, but 
the two cavities always communicate by a considerable opening 
through which the common portion of the external layers of the sacs 
passes. The change of the teeth commences aboiit the sixth or 
seventh year. The first great molaris is the first of the second set 
which appears, then follow the incisors and canine teeth, the penulti¬ 
mate molaris not till the thirteenth or fourteenth year, and the last 
molar between the sixteenth and twentieth year. ’ The roots of the 
milk-teeth are absorbed before they fall out. 
It has been frequently asserted that if the teeth of an animal, after 
being drawn, are re-inserted into their sockets, they will again take 
firm root. This appears to me very questionable. If a real organic 
union takes place in these experiments, it must be by the lacerated 
vessels of the pulp of the tooth uniting again with the vessels at the 
bottom of the socket. It is an interesting point which ought to be 
more accurately determined. A sure way of deciding the question 
would be, to feed animals, in which the teeth had been recently trans¬ 
planted, with madder. If any vascular connection had been formed, 
the innermost layer of the tooth towards the pulp would be coloured 
red. The teeth not being organised, fissures in them, of course, can¬ 
not be closed by the reproduction of new dental substance; they can, 
at most, be filled with crusta petrosa, or tartar from the salts of the 
saliva. In serpents new poison-fangs are being constantly repro¬ 
duced. The new teeth of the crocodile press forwards into the 
conical cavities of the old teeth, the posterior wall of which becomes 
absorbed. 
3. The crystalline lens.—It would appear that, in certain cases 
where the lens has been removed, it is reproduced by the capsule— 
its matrix. Leroy d’EtioIe has observed this.* In the first case, 
thirteen days had elapsed since the extraction of the lens when the 
eye was examined; in the second case, thirty-three days; in the third, 
thirty-nine days; in the fourth, thirty-one days; in the fifth, forty-six 
days; and in the sixth, one hundred and sixty-five days. The ex¬ 
periments were made on rabbits, cats, and dogs. The contents of 
the capsule were either a crumbly mass, as in the second case; or a 
small lenticular body, as in most of the other cases; but in the sixth 
case a full-sized lens was found.t 
* Magendie’s.Journ. de Physiol. 1827, 30. 
f See Mayer, Graefe in Walther’s Journ. xvii. 1. Vrolik, ibid, xviii. 4. W. 
Soemmering, Boebachtungen über die organ. Veränderungen im Auge, nach 
Staaroperationen. Frankfurt, 1828. *
        

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