tries, the real nature of the morbid change in which it essentially consists is a matter of doubt.'

Another circumstance unfavorable to the study of diseases of the liver is, that we can obtain but little direct evidence of its physical condition during life.

When the lungs are the seat of disease, we may discover, by the sense of hearing, whether any portion of them near the surface contains the natural quantity of air, or whether this, in whole or in part, be displaced by some denser matter; whether the surface of the pleura be roughened by fibrine, or its sac distended by fluid; whether the bronchial tubes be free, or more or less choked by secretions.

If the heart be the organ affected, we may not only trace its outline and estimate the strength of its ventricles, but, by the same sense, penetrate its interior, and ascertain the condition of its valves. The whole physical structure of the organ is, as it were, laid open to us.

We have it in our power indeed to explore the liver by touch and by percussion, but we cannot by these means of investigation penetrate its surface, and discover changes in its consistence and texture. They only enable us, in some cases, to trace its outline, to discover any striking inequalities of its surface, and to form a tolerable estimate of its bulk. This, indeed, is valuable information, and more than we can learn of the kidneys by similar means. But in investigating the diseases of the latter organs, we have the more than equivalent advantage, that day by day we can measure the quantity, and ascertain the composition, of the urine secreted; that is, we can tell precisely the manner in which their functions are performed.

The secretions of the liver, on the contrary, cannot be collected and analyzed during the life of the patient; indeed, until lately, they could scarcely be analyzed at all, as the most celebrated chemists were not even agreed as to what are the normal constituents of bile.

Thus, to detect and distinguish the diseases of the liver, practitioners had little more than the signs of functional disturbance— signs, in all cases, of doubtful import, and here, if we except that of jaundice, more than commonly obscure and equivocal. We cannot, then, feel surprised that our knowledge of these diseases should be more imperfect, our diagnosis of them less sure, and our treatment,

1 Since this was written, much has been done to elucidate the morbid changes in Bright's disease of the kidney: especially by Dr. George Johnson, whose admirable papers on this subject have been published in the Medico-Chirurgical Transactions.

consequently, more tentative and empirical, than of the diseases of any other organ of equal importance.

Very recently, two of the impediments to the study of diseases of the liver have been in some degree removed. By the researches of chemists we have obtained more precise knowledge of the composition and uses of bile; and by the labors of Kiernan and Bowman in this country, and of Müller and Henle in Germany, we have been taught the intimate structure of the organ; so that now, by the naked eye or the microscope, we can distinguish the various changes of its texture produced by disease.

It is impossible to explain or to understand the morbid appearances of the liver, without referring to its intimate structure, and as some points relating to this have been only lately made out, I shall commence with a short account of it.

Perhaps the best way to get an idea of the structure of the liver is to examine under the microscope,

1st. A thin slice of liver, in which the portal and hepatic veins are thoroughly injected.

2d. A small particle taken from the lobular substance of a fresh liver in which the blood vessels are empty, as in an animal killed by bleeding.

From the first specimen we may learn the distribution of the minute portal and hepatic veins, and the intermediate capillaries. The annexed wood-cut (Fig. 1) has been made from a portion of the liver of a frog, which I selected from numerous specimens of injected liver made by Mr. Bowman. It represents, on a magnified scale, a small branch of the hepatic vein, two or three small branches of the portal vein, and the intermediate capillaries. It appears that the capillaries have nearly the same relation to the branches of the portal vein as they have to those of the hepatic vein. It is difficult from this specimen to tell which branch is portal, which hepatic; the smaller branches of both being, as it were, hairy with capillaries springing directly from them on every side, and forming a close and continuous network.

If we imagine views similar to that in the wood-cut, made by slicing the liver in various directions through the branch of the hepatic vein, or through one of the branches of the portal vein, there represented, we shall perceive that the entire organ, abstracting the canals in which the trunk and branches of those veins run, is occupied by a

close network of capillary bloodvessels, continuous in every direction throughout its substance. The capillary vessels of this network immediately minister to the secretion of bile. The vessels of larger size serve merely to convey the blood to them, or carry it from them.

capillaries.

These capillaries are of comparatively large size, being always onethird wider than the diameter of the blood-globule, and sometimes nearly twice as wide, and their coats, which have no areolar tissue about them, appear very thin and delicate.'

But, although the capillaries form a continuous network throughout the substance of the liver, no part of the portal blood traverses the entire network. The whole mass of capillaries is divided by the minute branches and twigs of the portal vein into small, tolerably defined masses; and is likewise partitioned in a similar way, by the minute branches and twigs of the hepatic vein, which are intermediate to, or, as it were, dovetailed with, the branches and twigs of the

See an admirable article on "Mucous Membrane," by Mr. Bowman, in Todd's Cyclopædia of Anatomy and Physiology, in which several points in the minute structure of the liver noticed in this chapter were first published.

portal vein. In effect of this, the blood conveyed through any branch of the portal vein to a small mass of capillaries, having performed its part in secretion and been drained of the principles of bile, passes out of the liver through an intermediate or adjacent branch of the hepatic vein; so that the entire mass of capillaries is duly supplied with fresh portal, or biliary, blood.

In tracing even large branches of the portal and hepatic veins, it is seen that they generally run transversely, or that the directions of the two orders of vessels cross each other.

In consequence of this arrangement of the minute vessels, if we cut into a liver in which, as is usual after death, the branches and twigs of the hepatic vein, and the capillaries immediately terminating in them, are full of blood, while the branches and twigs of the portal vein and the capillaries immediately springing from them are empty, the cut surface will be mapped out into small, tolerably equal, and somewhat pentagonal, spaces, having the outline, formed by the portal twigs, pale, and the centre, into which a twig of the hepatic vein enters, red. The small masses, of which these pentagonal spaces are sections, have been termed lobules of the liver. They have been described by Malpighi, Kiernan, Müller, and others, as isolated from each other, and each invested by a layer of areolar, or, as it used to be named, cellular, tissue. In the pig, in which the lobules of the liver were first noticed, they are thus invested, but the injected preparations of Mr. Bowman show, I think, clearly, that in man, and in many other animals, they are not distinct, isolated bodies, but merely small masses defined more or less distinctly by the ultimate twigs of the portal vein and the injected or uninjected capillaries immediately contiguous to them. The ultimate twigs of the vein are, as it were, hairy with capillaries, springing directly from them on every side, and forming a close and continuous network. The lobules appear distinct isolated bodies only when seen by too low a power clearly to distinguish the capillaries.

The real nature of the lobules, and the manner in which they are formed, will perhaps be better understood by reference to the annexed wood-cut (Fig. 2), for which I am indebted to the kindness of Mr. Bowman. It represents on a magnified scale six lobules of the liver, and was made from a drawing under the microscope, of a section of the liver of a cat, partially injected through the portal vein, and also through the hepatic vein; a a a represent minute twigs of the portal vein injected; b bb, capillaries, likewise injected, immediately

springing from them, and serving with them to mark the outline of the lobules; d d d, capillaries in the centres of the lobules, injected through

the hepatic vein; e e, places at which the size injected into the portal vein has met that injected into the hepatic vein, so that all the intermediate capillaries are colored and conspicuous; 77, centres of lobules into which the injection has not passed through the hepatic vein.

It has been stated that the capillaries have nearly the same relation to the small branches and twigs of the hepatic vein as they have to those of the portal vein. This statement requires some qualification. The branches of the portal vein are each accompanied to their smallest twigs by a branch of the hepatic artery, and by a branch of the hepatic duct. These vessels, which are very much smaller than the corresponding portal vein, run up (as seen in Fig. 3') on one side of it, and of course on that side the capillaries do not spring so immediately from the venous trunk; in other words, the lobules are not in such immediate contact with the vein as on other sides. The

This diagram and the two following are copied from the admirable paper on the Liver in the Transactions of the Royal Society for 1833, by Mr. Kiernan, to whom we are in great part indebted for the exact knowledge we now have of the distribution of blood vessels in the liver, and of many other points of its structure.