prevent adhesion, the next step is to pack them with elastic rubber. This is very easily accomplished: the two side-pieces, being adjusted to the base, are kept firmly in position by an iron clamp, and the rubber packed in from above. When there appears sufficient, the top is put on, and the whole screwed tightly together, being put on a hot plate for a few minutes to soften the rubber. The casts are then taken apart, any excess removed, or any deficiency filled up. They are again screwed up and fitted in an iron framework, with wedges to secure them, and put into the vulcanizer. In reference to the rubber to be used, there can be no question that that which is prepared by Messrs. Ash & Sons is by far the best, both as regards quality of materials and

wear.

If this description of rubber be used, the time for vulcanizing is six hours; that is to say

2 hours at 240°.

2 hours at 250°.

2 hours at 260°.

This will produce an artificial velum of the greatest elasticity and power of resistance to the acids of the mouth. It has occasionally been a subject of inquiry as to the description of vulcanizer we use; we have therefore obtained a drawing of one from the maker, Rutterford, of Poland Street, with a description of its different novelties. We use the largest size made, and

place the mould for vulcanizing as near the centre as possible. Having tried several descriptions of boilers, we find this the most satisfactory (fig. 18).

The boiler is of copper a quarter of an inch thick, and five inches in diameter. It is made for one, two, three, and four flasks, with the ordinary rings. Each boiler is properly tested and stamped. No washer, or india-rubber ring required. One screw only (B) to tighten the lid. D is a let-off tap for steam. The safetyvalve is thereby preserved, and is not liable to get out of order. The lid contains a thick lead collar, which does not require renewing. It can

be used with a steam gauge (C) if preferred, or with the ordinary thermometer (A), or both. It is equally adapted for alcohol or gas.

The adjustment of a front piece to keep the velum in the cleft will depend on the state of the teeth. If they are all perfect, a simple suctionplate, as shown in page 75, fig. 23, is all that is necessary. If any teeth should be wanting, artificial ones to supply their place should be mounted on the front piece, as in an ordinary set of teeth; and if there be any deformity of the hard palate, as in most cases there is when associated with hare-lip, it will have to be restored and made as symmetrical as possible by additions to the hard rubber. When, however, the anterior portion of the mouth is perfect, the palate should be made as thin as possible, and not extend further back than the second bicuspids.

E

CHAPTER VI.

ON THE INTRODUCTION OF THE INSTRUMENT INTO THE MOUTH. SUBSEQUENT TUITION. VALUE OF SINGING IN FACILITATING THE PROPER USE OF THE PARTS. IMPEDIMENTS TO PRODUCTION OF PERFECT VOICE.

THE artificial palate and velum being completed, the next step is its introduction into the cleft. This is sometimes the source of a little difficulty in very nervous subjects, as the presence of the foreign body (though the mouth will by this time have become less sensitive) cannot be borne under all circumstances with patience.

It is well to try in the elastic velum alone in the first instance, having it attached to a long piece of stout platina wire, one end being fitted into the pinhole previously mentioned. This will allow of its being passed well down at the back of the mouth, in order to get the wings or flaps into their proper relative position without much strain on the soft parts, while, on account of the length of the wire, the operator is able to see well what he is about. The velum can then be drawn forward into its proper place, and held there firmly for a minute, or longer, if the patient can bear it.