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BEALE, ON THE MICROSCOPE. 47 
The seventh lecture is devoted to the examination of tis- 
sues, and their preservation as permanent objects. Although 
the preservation of specimens is undoubtedly secondary to 
the accurate observation of facts, every microscopist must 
find it advantageous to keep specimens for reference, and 
where systematic teaching in histology is the object, it can 
scarcely be effected at all without a good collection of speci- 
mens. Hence the value of this lecture. The succeeding 
lecture is devoted to the same subject ; the method of pre- 
paration being that of injection. On this subject Dr. Beale 
is an authority. He has been so successful in injecting the 
ducts of the liver, that we give his experience on this subject : 
“The modes of injecting which we have just considered, although appli- 
cable to the injection of vessels, are not adapted for injecting the ducts and 
glandular structure of glands; for as these ducts usually contain a certain 
quantity of the secretion, and are always lined with epithelium, it follows 
that when we attempt to force fluid into the duct, the epithelium and 
secretion must be driven towards the secreting structure of the gland, which 
is thus effectually plugged up with a colourless material, and there is no 
possibility of making out the arrangement of the parts. In such a case it 
is obviously useless to introduce an injecting fluid, for the greatest force 
which could be employed would be insufficient to drive the contents through 
the basement membrane, and the only possible result of the attempt would 
be rupture of the thin walls of the secreting structure and extravasation of 
the contents. As I have before mentioned, partial success has been obtained 
by employing mercury, but the preparations thus made are uot adapted for 
microscopical observation. 
**T have long felt very anxious to inject the ducts of the liver in order to 
ascertain the manner in which they commenced in the lobule, and the 
precise relation which they bore to the liver cells. This has long been a 
point of dispute among microscopical observers, and many different and 
incompatible conclusions have been arrived at by different observers. In 
order to prove the point satisfactorily it was obviously necessary to inject 
the ducts to their minute extremities, which no one, as far as I was able to 
ascertain, had succeeded in doing satisfactorily. After death the minute 
ducts of the liver always contain a little bile. No force which can be em- 
ployed is sufficient to force this bile through the basement membrane, for it 
will not permeate it in this direction. When any attempt is made to inject 
the ducts, the epithelinm and mucus, in their interior, and the bile form 
an insurmountable barrier to the onward course of the injection. Hence it 
was obviously necessary to remove the bile from the ducts before one could 
hope to make a successful injection. It occurred to me, that any accumu- 
lation of fluid in the smallest branches of the portal vein or in the capillaries, 
must necessarily compress the ducts and the secreting structure of the liver 
which fill up the intervals between them. The result of such a pressure 
would be to drive the bile towards the large ducts and to promote its 
escape. Tepid water was, therefore, injected into the portal vem. The 
liver became greatly distended, and bile with much ductal epithelium flowed 
by drops from the divided extremety of the duct. The bile soon became 
thinner owing to its dilution with water which permeated the intervening 
membrane, and entered the ducts. These long, narrow, highly tortuous 
channels were thus effectually washed out from the point where they com- 
