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at the same time transparent. A thin section is to be made with a very sharp, thin knife, then slightly washed and examined in dilute alcohol or glycerine. In many of the sections thus prepared, the appearances represented in some of the drawings in the present volume were produced. The same success is by no means always met with, and it is necessary to examine numerous specimens treated in different ways. Some of my preparations were obtained from the livers of animals in which the duct had been tied some hours before death; and others were taken from organs into the duct of which injection had been gradually forced until it would contain no more. Small pieces were then hardened, and examined after the lapse of some time.

But, although, in many instances, I was able to satisfy myself of the truth of the most important points which I have to bring forward with regard to the arrangement of the minute ducts, a vast number of the preparations failed altogether, and I could not demonstrate the arrangement in every liver which I tried, so that I was compelled to resort to new means of preparation. Injection I had tried many times, and had only succeeded so far as consisted in driving the bile into the small ducts. I could not force the injection far enough. The injection usually only reached the surface of the hepatic cell-containing network, and, in many instances, accumulated at this point, in which cases, the appearance of a duct terminating in a blind extremity was produced.

Method of Injecting the Ducts of the Liver, and the Hepatic Cell-containing Network.-Although I felt certain of the correctness of my observations upon uninjected specimens, it appeared to be absolutely necessary to inject both the ducts, and from these, the cell-containing network, before their continuity could be regarded as proved. The presence of the bile in the ducts always prevented the passage of the injection into their most minute ramifications, and no long continued pressure, which I applied by means of a high column of fluid, or with a syringe, was sufficient to force this bile through the thin walls of the duct, and give place to my injection. A most imperfect injection or rupture was the invariable result. After some time it occurred to me to endeavour in the first place to force out the bile by injecting the vascular capillaries with water, and, to my great delight, in the

very first specimen I tried, the gall bladder filled with bile soon after the injection of the portal vein had been commenced, and bile also escaped from the common duct. After a short time, almost pure water ran out from the duct. The water was allowed to escape from the vessels, and then the liver placed in cloths to soak up the water with which it was saturated. The duct, after the lapse of a few hours, was injected. I have examined the water which escaped from the duct upon several occasions. It always contained a large quantity of cylindrical epithelium, and sometimes circular cells from the small ducts were found; but I have never met with specimens of liver-cells, which is easily accounted for, when we consider the small calibre of the smallest ducts. In rare instances these are, no doubt, much larger than natural, in which case the entrance of the hepatic cells would not be prevented. I see, therefore, no reason to doubt the accuracy of Mr. Wharton Jones's observation, although I am unable to confirm it from actual observation.

The injection passed into the ducts very readily and with slight force; and could be seen entering the lobules upon the external surface. It did not appear gradually round the circumference of the lobule, as is the case when the portal vein is injected, but it formed small roundish points, to the unaided eye, almost like little extravasations, here and there at the outside of the lobules; and it then spread for a short distance towards the central part. Upon examining a small piece with the microscope, the small ducts were well seen, and it was evident that they not only went up to the lobules, but that they penetrated into their substance.

Transparent Injections. Although the injection evidently had not extravasated, the outline of the network was not distinct, and upon examining thin sections with a quarter, only a confused appearance was visible, and I was unable to demonstrate the relation of the cells to the ducts and to the vessels. Before I could hope to make out this point, it was clearly necessary not only to inject the ducts, but to inject them in such a manner that they would bear examination with the higher powers (at least a quarter). After trying unsuccessfully many opaque injections, it occurred to me that a transparent injection might succeed better. Camboge, Carmine, Cochineal, Lake, and some other colouring matters were

employed, but the injection permeated the delicate basement membrane of the tubes and the adjacent textures were equally coloured, so that the nature of the arrangement was still undecided. Freshlyprepared Prussian blue was tried, and with much better success. Now, however, a new difficulty presented itself. The thinnest sections which could be obtained, necessarily consisted of several planes of the cell-containing network and capillaries, and, in consequence of the distension of the former by the injection, the latter could not be distinguished. It then occurred to me to try to inject both the portal vein and the duct; the former with plain size, and the latter with Prussian blue. In a liver prepared in this manner I was fortunate enough to see in several different sections, with a quarter of an inch, the blue transparent injection in one tube in close juxtaposition to a colourless capillary vessel injected with plain size. By varying the kind of injection, and resorting to many experiments which it would be useless to recount, I have gradually arrived at a plan of procedure by which specimens can almost always be obtained which will bear examination with a quarter, or even with an eighth of an inch object glass.

Extravasation into the Lymphatics.-Often when too great force is employed, rupture of the walls of a small duct occurs, when the injection not unfrequently passes into a lymphatic vessel, and in this way, as was shown by Kiernan, the abundant plexus of lymphatics in the large portal canals can be injected. In one instance the injection passed into the thoracic duct. A similar result likewise occurred to me in a rabbit. This accidental injection of the lymphatics has been noticed by many. Mascagni long ago noticed that when injection was thrown into the ducts it returned colourless by the absorbents. Although the lymphatics are so easily injected, I have not been successful in my attempts to ascertain how these vessels commence in the liver, and have not yet seen them distinctly in portal canals less than the quarter of an inch in diameter.

DIRECTIONS FOR INJECTING A LIVER FOR EXAMINATION WITH HIGH POWERS OF THE MICROSCOPE.

The portal vein is to be injected with tepid water until the blood is washed out and the whole organ becomes nearly colour

less. After a time water only slightly tinged with blood will escape from the hepatic vein, while at the same time almost pure water will pass out from the gall duct. The force used must be as gentle as possible, for otherwise some of the minute vessels will be ruptured, and the preparation will not succeed. After the vessels have been fully distended in this manner, the water is allowed to escape from them, and the liver wrapped up in two or three soft cloths, which will absorb much more of the water. The cloths are to be changed when soddened with water. In the course of from twelve to twenty-four hours, the liver will appear shrivelled, and of a soft clayey consistence. It is now ready to be injected from the duct. A mixture of about two-thirds water, and one-third spirit, in which recently precipitated Prussian blue is suspended, is strained through two or three layers of the finest muslin, and carefully injected into the duct, applying slight, but gradually increased, pressure. The injection should be performed with a small half-ounce or ounce syringe, or by pressure of the fluid placed in a glass tube about four feet high.

As soon as the blue injection is seen at several points at the circumference of the lobules, and more fluid cannot easily be forced into the duct, it is better to wait a few hours, and then inject a little more; but the injection of the duct must not be pushed too far, for although in some places no colour whatever is to be seen, in other parts a good injection has, perhaps, been effected. After the duct has been injected, the liver is again set aside for a few hours in damp cloths, so that the superfluous fluid may be absorbed.

Preparation of the Injection.—The Prussian blue is prepared in the usual way, by adding gradually a solution of Ferrocyanide of Potassium to a very dilute solution of Perchloride of Iron. The mixture should be of a dark colour, but should contain no flocculi. It should not deposit a precipitate even after it has been allowed to stand for some time. Without care an abundant deposit of Prussian blue is obtained, which does not flow well. The mixture should have the appearance of a dark-blue solution, rather than of a deposit held in suspension. The addition of a little spirit has the advantage of hardening the delicate walls of the smaller ducts as the injection passes into them, and thus preventing their

rupture. The great advantage of the Prussian blue arises from the circumstance that the precipitate is so fine as to appear like a solution; but still the minute particles cannot be made to pass through the basement membrane of the ducts.

The addition of glycerine to this fluid causes it to flow better. The following is the composition of the injecting fluid which I have been lately in the habit of using. It is well adapted for all ordinary purposes of injection. It is used cold, and it does not run out from the openings of the divided vessels when a thin section is made-a disadvantage from which few injecting fluids which can be used cold are free.

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The Ferrocyanide of Potassium is to be dissolved in an ounce of the water, and the Tincture of Sesquichloride of Iron added to another ounce. These solutions are to be mixed very gradually, and well shaken in a bottle, the iron being added to the Ferrocyanide of Potassium. When thoroughly mixed these solutions should produce a dark-blue mixture, in which no precipitate or flocculi are observable.

The naphtha is to be mixed with the spirit; and the glycerine, and the remaining two ounces of the water added. It is important to mix the solutions in the above order, for otherwise a dense precipitate and free flocculi which will not run well are formed.

Lastly, the colourless fluid is to be mixed gradually with the Prussian blue, the whole being well agitated in a large bottle during the admixture.

Injection of the Portal Vein and Hepatic Artery with plain Size. -After the duct has been injected in the manner above referred to, the liver is placed in warm water, and when it has become warm through the portal vein and hepatic artery are to be injected with fine size. If the injection of the duct has been well conducted,

* The Tinct. Ferri Sesquichlor. of the London Pharmacopoeia, commonly known as Muriated Tincture of Iron, is recommended because it is a solution of a persalt of Iron, which can always be readily obtained of uniform strength,

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