8 METHOD OF TAKING IMPEESSIONS 



well known to us all. I therefore constructed a 

 tray, wliich, while it secured these points, gained 

 another of considerable importance ; viz. that of 

 forcing the wax not only upwards, but forwards 

 into the intervals between the rugae. The diffi- 

 culty, I may say impossibility, of efiecting this by 

 the ordinary tray must be evident to every one 

 accustomed to its use ; with it the wax is merely 

 driven upwards, whereas it is necessary that it 

 should have also a forward direction. It first 

 struck me that a tray, nearly similar to those 

 generally used for the lower jaw, with its inner 

 border nearly perpendicular, would answer the 

 purpose, so that when the wax rose above the 

 inner border, as it would do when pressed against 

 the alveolar ridge, it could be pressed upwards 

 and forwards with the index finger, and thus be 

 forced firmly into the interstices of the rug^ and 

 against the roof of the mouth ; but I found that 

 the point of my finger was not broad enough to 

 make the pressure equal on all sides at once, and 

 that when I pressed on one side, the wax rose at 

 the expense of the other, and that when I with- 

 drew my finger before removing the impression 

 from the mouth, the wax was sucked down a little 

 by the finger. These objections were immediately 

 overcome by substituting a piece of metal rather 

 broader than the interval left in the tray for the 

 tongue, which I attached by a hinge to the inner 

 border of the tray behind the incisor teeth. After 



