distribution of blood is impeded and nutrition impaired; and it occurs from arterial obstruction caused by a mass of fibrin or a vegetation derived from the left side of the heart, constituting what is called an embolus or plug. Softening, as thus produced, as will be hereafter seen, is involved in the causation of apoplexy and paralysis.

Softening is incidental to inflammation affecting any of the tissues. This result is especially marked in inflammation of the mucous membranes. These are sometimes completely disorganized and reduced to a pulp, so that portions are mechanically removed by the attrition of substances moving over their surfaces. This is seen in examinations after death in cases of dysentery. When the degree of softening of the mucous membranes is less, it is shown by the inability of tearing small portions away in strips with the forceps. Non-inflammatory softening of these membranes, elsewhere than in the stomach and small intestines, is certainly rare. And in the stomach, especially, the softening found after death, when inflammation has not existed, is, in most cases, probably, a post-mortem change due to the dissolving action of the gastric juice. Softening from the latter cause may exist in a great degree, affecting all the coats of the stomach, leading to perforation and softening of the adjacent viscera, in cases of death taking place suddenly while the process of digestion was going on. As the protection of the stomach against the action of the gastric juice, in life, has been shown to depend on the presence of mucus, it is not improbable that softening from the same cause may sometimes take place before death, owing to deficiency of the secretion of mucus. Softening occurs not only in parts which are inflamed, but in proximate tissues not involved in the inflammation. Thus, in serous inflammations, the subserous areolar tissue loses its normal firmness and becomes brittle, so that the membrane is detached much more easily than in its healthy condition.

Softening of the muscular tissue is incidental to fatty degeneration, but it occurs as the chief or sole palpable change in the heart, in certain cases of typhus and typhoid fever. Softening of the spleen, occurring in these fevers, is also an example of this change occurring without inflammation, or any well-defined change in composition or structure.

The softening which is non-inflammatory and independent of other palpable changes is, in general, referable to a defect in the nutrition of the affected parts. This defect may be dependent on circumstances limited to the parts, as when cerebral softening arises from arterial obstruction; or it may proceed from a general condition, involving a deficiency of nutritive supplies in the blood, as when softening of the heart occurs in typhus or typhoid fever. If the softening consist only in diminished coherence of the component anatomical elements of the parts, without being sufficient to occasion disorganization, it is not irremediable nor necessarily even a grave lesion. Softening of the heart and spleen doubtless occurs in cases of fever which end in complete recovery; and it is not improbable that in certain cases of softening of the brain, dependent on a temporary defect of arterial supply, for example when occasioned by an embolus, the normal consistence may be restored after the re-establishment of the circulation.

СНАРТER II.

ANATOMICAL CHANGES IN THE SOLID PARTS OF THE BODY-(CONTINUED.) Lesions of Composition-Exudations and Transudations-Fibrinous Exudation or Coagulable Lymph-Tuberculous Exudation-Scrofula-Carcinoma or Cancer-Typhoid Deposit.

ALTERATIONS as regards the composition of parts constitute the third class of anatomical changes. The lesions embraced in this class are more numerous and important than those included in the preceding classes. I shall notice the changes belonging to this class, which are of importance in relation to medicine as distinguished from surgery, presenting, briefly, certain distinctions, etc., which should be understood by way of preparation for entering on the study of individual diseases. It does not fall within the scope of this work to enter into either a comprehensive or minute account of the various alterations which will be noticed. The student is expected, in addition to the outlines here presented, to pursue this part of the subject more fully by means of works which treat at length of morbid anatomy and general pathology.

It will be appropriate to reckon among changes in composition, not only perversions of structure, but changes which consist in the addition of abnor mal deposits, either solid or liquid, leaving the tissues of the parts unaffected. For example, the infiltration of liquid into the interstices of a part alters its composition, although there may be no structural change in the part. To cite another example, in the hepatization which takes place in pneumonitis, there is a solid deposit within the air-cells, and the presence of this deposit alters for the time being the physical condition of the affected portion of lung. The composition of the lung is in fact changed. But the normal structure of the lung remains intact, and so soon as this morbid deposit disappears, the normal condition of the lung is restored. On the other hand, there are changes in which morbid deposits supplant the substance proper to the parts affected, and thus involve perversions of structure. Here is an important distinction as regards changes in composition. Changes in composition may consist, then, in the presence of a morbid deposit of some kind, without change of structure, or they may consist in structural alterations. The latter are to be distinguished as lesions of structure, or, as they are commonly called, degenerations. Changes which do not affect the structures entering into the composition of parts are not necessarily destructive; they may be temporary, and after their disappearauce the parts may be in no wise damaged, as in the example of pneumonitis. But lesions of structure or degenerations involve disorganization of parts, and in general are permanent or incurable.

A distinction is to be made between deposits or morbid products which by a process called coagulation assume a solid form, and those which remain in a liquid state. The source of both, of course, is the blood, and the former, as well as the latter, must, of course, be in a liquid form when first deposited. Coagulated products, therefore, have assumed a solid form after escaping, as liquids, through the coats of the vessels. For the sake of distinction, the term exudations should be restricted to coagulated deposits or products, applying the term to the exuded matter, or the term exudates may be used.

On the other hand, the term transudations may be applied to constituents of the blood which escape through the coats of the vessels and preserve their liquid state. These terms will be used hereafter as now defined. An exudation, or an exudate, is a coagulated deposit or product derived from the blood; a transudation is a liquid effusion constituting, when retained in any part, a dropsy.1

With the previous preliminary explanations, the consideration of the anatomical changes belonging to the third class will embrace coagulated deposits or exudations, transudations or liquid effusions, lesions of structure or degenerations; and added to these are new formations or morbid growths, pneumatoses or the abnormal presence of air or gas in parts, and parasitic productions vegetable and animal. The remainder of this chapter will be devoted to anatomical changes dependent on exudations.

FIBRINOUS EXUDATION.

An exudation which forms an important event in the natural history of certain inflammations is that distinguished as fibrinous. By the older writers this deposit was called coagulable lymph, and it is still commonly known by that name. Bennett calls it simple exudation. It is generally considered to be essentially the fibrin of the blood or the blood-plasma, either simple or more or less modified, in a coagulated state. The liquor sanguinis, which contains fibrin in a liquid state, exudes, and the fibrin coagulating constitutes the deposit. It may also be distinguished as inflammatory exudation. Existing without the vascular system, and independently of hemorrhage, it is always a product of inflammation; that is, it occurs only as a result of an inflammatory process. Hence it is the criterion by which the existence of inflammation in certain structures is determined; its presence is proof that inflammation existed in these structures, and, if not found on examination after death, adequate evidence of inflammation is wanting. It belongs especially to inflammation of the serous membranes, and will be found to constitute an important part of the history of pleuritis, pericarditis, peritonitis, &c.

Examined shortly after it has exuded upon a serous surface, it presents the appearance of a semi-transparent, gelatinous semi-solid. Examined microscopically it is found to contain minute filaments such as are found in the coagulated fibrin of the blood, intermingled with corpuscles to which various names have been applied, viz., plastic, pyoid, exudation corpuscles, etc. They are regarded by Robin as belonging to a class of corpuscles called leucocytes, embracing pus globules, the white globules of the blood, mucous corpuscles, etc., all of which, according to this distinguished anatomist, are essentially identical. At a later period the exudation becomes more solid, frequently forming a thick, dense layer adherent mechanically to the serous surface, and forming distinctly a fibrous arrangement. Detached and peeled off, it resembles a membrane, and is commonly called a false membrane. Not unfrequently this is found to consist of a series of layers which may be separated from each other like the coats of an onion. The coagulation of the fibrin contained in the exuded liquor sanguinis leaves a certain amount of serous liquid which, in serous inflammations, accumulates within the sac, so that in examinations after death more or less liquid is usually found together with the coagulable lymph. Flakes of lymph, in greater or less abundance, are contained in the liquid, and the latter is turbid, not transparent, as in purely dropsical effusions.

'This distinction between an exudation and a transudation is not made by all writers. It is made especially by Lehmann.

In the progress towards recovery, the liquid contained within the serous sac is absorbed. The serous surfaces then coming into contact are first agglutinated by means of the intermediate lymph. The latter is absorbed more slowly. A true membranous or organized structure then becomes developed, which is the medium of the permanent adhesions resulting from inflammation of serous structures. An unfavorable progress is characterized by the serum and lymph remaining unchanged for an indefinite period, or by the production in large quantity of the well-known liquid called pus, which contains in abundance the corpuscular bodies called pus globules or leucocytes.

Selecting serous inflammations as typical, because they are characterized by the constancy and abundance of inflammatory exudation, the brief description just given is an epitome of the natural history of this morbid product. But considerable variations are observed in different cases of serous inflammations. The relative proportions of lymph and serum vary widely. The quantity of lymph may be abundant or quite small, and the same is true of the liquid effusion. The constitution of the lymph varies. The formation. of fibrillæ, or the fibrillation, may be greater or less, and the corpuscular constituents may be few or abundant. Paget reckons two varieties of lymph, one variety being characterized by the predominance of fibrillæ and the other by the abundance of corpuscles, with a small proportion of fibrillæ. The former he calls fibrinous, and the latter corpuscular, lymph. The fibrinous variety he regards as favorable for the production of organized tissue, while the corpuscular variety tends to the production of pus or suppuration.

The ordinary product of inflammation of mucous membranes is mucus variously modified, and containing, in more or less abundance, the corpuscular bodies known as mucous globules, which are essentially identical with pus globules, or, in other words, belong in the category of leucocytes. Exceptionally, however, fibrinous exudation occurs on a mucous surface, and, disposed in the form of a false membrane, presents characters analogous to those which belong to the exudation in serous inflammations. This constitutes the characteristic feature of the inflammation of the larynx and trachea, sometimes extending to the bronchia, in true croup, and of the inflammation of the fauces, air-passages, and in other situations in the epidemic disease called diphtheria. Inflammation of a mucous surface or of the skin, when characterized by fibrinous exudation, is frequently distinguished as diphther itic, after a term introduced by Bretonneau. Occasionally in bronchitis a false membrane is formed, and this variety of the disease is called plastic bronchitis. Fibrinous exudation is not uncommon in cases of dysentery. The formation of new tissue, that is, of organic structures, does not take place in connection with a fibrinous exudation on mucous surfaces. The false membrane, in all cases, in the course of a few days becomes detached by a suppurative process beneath it and is thrown off. This is the basis of a division, by Rokitansky, of inflammatory exudation into croupous and plastic. The term plastic, frequently applied to inflammatory exudation, denotes its capacity of developing within it organized structures. This is also expressed by the term blastema which is frequently applied to inflammatory exudation. The term cytoblastema, which has the same application, denotes the development of cell. formations within the exudation.

In pneumonitis it is inflammatory exudation within the air-cells which solidifies the lang, giving rise to the condition called hepatization. In this situation organic tissue is not formed, and the exudation is removed by absorption. A very small proportion, sometimes none whatever, is expectorated, and clinical observation shows that the large amount of exudation which takes place in this disease may be absorbed very rapidly, being all

removed in the course of a few days. In other parenchymatous inflammations, fibrinous exudation sometimes takes place and is infiltrated among the component tissues. In the brain and spinal cord it is presented in the form of minute granules with which are combined pus globules or leucocytes. These appearances, in connection with softening, show that the latter is due to inflammation. In other parts the presence of fibrinous exudation, which may persist without metamorphosis or change for an indefinite period, involves enlargement by false hypertrophy and induration; or it may sooner or later lead to suppuration; or, leading to the development of fibroid tissue, it may produce atrophy and disorganization, as is seen in cirrhosis of the liver and the hard contracted kidney.

It is thus seen that the fibrinous exudation in different situations, and in the same situation in different cases, presents variations as regards its constitution, the metamorphoses of which it is the seat, its behavior (to borrow a metaphorical term from the chemist), and its consequences. Our present knowledge does not enable us to say to what extent these diversities may be due to primary, essential differences, that is, differences pertaining to the exudation itself, or how much is attributable to circumstances connected with the exuding process, or again, the amount of influence exerted by the surrounding parts upon the exudation after it has taken place. Much undoubtedly depends on the situation of the exudation; for example, it is never the seat of newly formed organized structures on a mucous surface. But it remains to account for the variations which are shown in different cases in the same situation, for instance on a serous surface. With reference to these diversities, as well as to the different exudations, the view taken by Rokitansky is, that they represent corresponding diversities pertaining to the fibrin contained in the blood. The blood-changes which are supposed thus to account for differences as regards the local products of disease, this author calls the crases of the blood. Each of the different exudates, or the different varieties of the same exudate, in other words, has its own particular blood-crasis. This doctrine of crases, although perhaps rational, and sustained by cogent arguments, is neither demonstrable nor logically proven, and, for the present, must be considered as hypothetical.

A pathological question which must for the present be considered as sub judice relates to the development of organized tissue, and the production of corpuscular bodies in connection with fibrinous exudation; in other words, to this exudation regarded as a blastema (collectively, embracing other exudations, blastemata), or as a cytoblastema. The question is, whether the newly developed tissues, which are undoubtedly produced, and pus globules, are products of a metamorphosis of the coagulated fibrin or lymph; in other words, is the coagulated fibrin or lymph converted into living structure, does it take on organization, and is it transformed into pus? The view taken by Paget, and generally received by pathologists, is, that the coagulated fibrin or lymph is organizable, i. e., capable of being transformed into organized living structures; and also that, by a kind of degenerative change, it is formed into pus. The term plastic is used to distinguish the kind of lymph which is supposed to be especially prone to organization. On the other hand, Robin and others regard coagulated fibrin or lymph in the light of an extraneous product, denying its capability to be transformed either into organized tissues or pus. According to the latter view, it either remains without essential change, or it is exfoliated, or it is absorbed, newly formed tissue being produced by molecular combination during the act of exudation; consequently, that alone it has no claim to be called a blastema, nor does it take part in the generation and multiplication of pus globules or leucocytes.

The term crasis signifies mixture.