48 BEALE, ON THE MICROSCOPE. 
menced as tubes not more than 1-3000th of an inch in diameter, to their 
termination in the common duct, and much of the thick layer of epithelium 
lining their interior was washed out at the same time. The water was re- 
moved by placing the liver in cloths with sponges under pressure for twenty- 
four hours or longer. All the vessels and the duct were then perfectly 
empty and in a very favourable state for receiving injection. 'The duct was 
first. injected with a coloured material. Freshly precipitated chromate of 
lead, white lead, vermilion, or other colouring matter may be used, but for 
many reasons to which I have alluded, the Prussian blue injection is the 
one best adapted for this purpose. It is the only material which furnishes 
good results when the injected preparations are required to be submitted to 
high magnifying powers. Preparations injected in this manner should ke 
examined as transparent objects.* They may be mounted in the ordinary 
penne fluids or in Canada balsam, but glycerine forms the most satis- 
actory medium for their preservation. A specimen of the ducts injected in 
this manner has been placed under the microscope, and specimens of the 
portal vein, of the ciliary processes, of the choroid, of the kidney, and some 
other tissues injected with the Prussian blue mixture, have been arranged 
for examination.” 
The last lecture is devoted to the advantages of chemical 
reagents im microscopical investigation. Here again we 
meet Dr. Beale on ground peculiarly his own. There can be 
no doubt that the necessity for a tedious chemical investiga- 
tion may be often avoided by the application of reagents to 
microscopic objects. Indeed, in some cases, where objects are 
altogether too small for chemical analysis in the laboratory, 
their composition may be known by observing the action of 
reagents under the microscope. As an instance of the value 
of the instructions in this part of the work, take the fol- 
lowing : 
“Testing for Carbonate and Phosphate of Lime, Phosphate of Ammonia-and- 
Magnesia, Sulphates and Chlorides—Now suppose I wish to ascertain the 
nature of the substances composing this earthy matter. I take a small por- 
tion, about the size of a pin’s head, place it upon this slide, and cover it 
lightly with a peice of thin glass. Next, I expel a drop of nitric acid (by 
warming in the hand the bottle with the capillary neck) close to the thin 
glass. The acid soon reaches the sediment, and now, one may observe the 
disengagement of a few bubbles of gas, which are, as it were, temporarily 
pent up by the thin glass, and prevented from escaping. If there should be 
any doubt of the action of the acid, we may resort to examination in the 
microscope, when, if there be very few bubbles, they may be detected. In 
this deposit carbonates are present. 
“The acid solution is now neutralized with ammonia. A faint flocculent 
precipitate is produced. After this has stood still for a few minutes it is 
covered with thin glass and examined under the microscope. It will be 
seen to consist of amorphous granules (Phosphate of Lime) and small 
crystals, which, if alowed to stand long enough, will take the form of trian- 
gular prisms (Phosphate of Ammonia and Magnesia). 
“If we wish to ascertain the presence of sulphates, a little of the nitric 
* “On the Anatomy of the Liver of Man and Vertebrate Animals.’ 
London: John Churchill, 1856. 
