23 
Haselwood, at the previous meeting, Dr. Hallifax and Mr. Wonfor 
gave a practical lesson to the Members present on Fluid Mounting. 
It was first pointed out that failure in securing permanence and 
freedom from air-bubbles was not confined to slides mounted by 
amateurs, but was a common fault in the preparations of some pro- 
fessional mounters, notable examples of such failures being handed 
round for inspection. 
Among the chief causes of the presence of air-bubbles was either 
a want of perfect union between the cell and the slide, or imperfection 
in the mode of fixing the covering glass. This was seen in glass cells 
in a less degree, but more so in the various substitutes for glass of a 
more or less porous character. The same remark applied to the 
shallow cells made with cement, and the turntable; the cause of 
failure in each case arising from a want of union between the slide 
_and the cell. : 
Another cause of failure was a want of flatness in the cell ; in the 
case of glass and some other substances it was difficult to grind down 
to a flat surface, but with cells made of the materials they had used 
for years a perfectly flat surface could be easily obtained. There was 
one caution very necessary to beginners, and a neglect of which was 
a very fertile source of failure. Never hurry the operation in mount- 
ing. It was also well to allow the object to steep for some time in the 
fluid in which it was intended to preserve it. By this means the fluid 
penetrated into the object, and the after-presence of air-bubbles in the 
mounting was often avoided. In some cases-steeping in alcohol, the 
application of gentle heat or the use of the air-pump was very advan- 
x tageous, though the last-named might be dispensed with by allowing 
more time. 
~ When the object was placed in the cell it was found advisable to 
heap up the fluid, and then to place the covering glass on it as 
E horizontally as possible. 
The making of deep and shallow cells, with modes of fixing them 
_ on the glass slides, and the different kinds of fluid best suited for different 
_ classes of objects, with the method of manipulation were practically 
_ shown by both gentlemen mounting different objects in deep and 
shallow cells, many hints being given at the same time on the prepa- 
- ration of cells and objects. 
