100 
tlie structure of the rods by imbedding a specimen of No. 
II. in Canada balsam so as to leave only one-half exposed, 
and then to etch away this upper portion by means of 
hydrofluoric acid. This method succeeded pretty well, 
oivino' a sectional view of the internal structure of the rod, 
O O J 
as shown in Fig. 7. The layers are seen by this method to 
be pretty clearly marked, but the etching is very irregular. 
The next method tried was rendering the opalescent 
nodules transparent by means of high-pressure steam, or 
rather water, as the substance was always surrounded by 
water, even when the temperature rose to 150°C. A 
fractured rod (Fig. 2), thus rendered transparent, shows on 
the fracture plain markings of the layers composing the rod 
cylindrically arranged, It was found that when a rod was 
