SEROUS AND SYNOVIAL MEMBRANES. 



533 



To these physical differences accede equally 

 important pathological grounds of discrimina- 

 tion. The effusion of the fibrinous fluid is 

 usually attended by more or fewer of those 

 symptoms, the aggregate of which is known 

 by the name of inflammation ; and in the few 

 instances where these external indications are 

 absent, the presence of the fluid is itself con- 

 sidered sufficient evidence of the previous oc- 

 currence of the inflammatory process ; while 

 the mechanical causes, which often appear 

 mediately or immediately to determine the 

 occurrence of the simply albuminous effusion, 

 seem to have no influence in the production 

 of these phenomena. Lastly, the fibrinous 

 effusion is distinguished by this important 

 quality, that it is susceptible of organization, 

 or capable of an apparent conversion into 

 tissues, the structure of which closely approxi- 

 mates to that of some one or other of the 

 normal and permanent textures of the human, 

 body. 



The class of effusions characterised by the 

 possession of the common properties of fibri- 

 nous composition, inflammatory origin, and 

 susceptibility of organization, is a very large 

 one, and includes a great variety of fluids. 

 The extremes of these numerous gradations 

 offer some contrast ; in one the symptoms of 

 inflammation are well marked, and the effusion 

 chiefly consists of matters which are plastic : 

 i.e. which pass rapidly from a fluid state, 

 through that of an uniform pasty mass, into a 

 solid form ; and which for the most part ex- 

 perience a rapid and complete organization, 

 being converted either into pus or into some 

 more permanent structure. In the other sub- 

 division, the symptoms of inflammation are 

 usually less marked, the fluid contains less 

 fibrine, is less susceptible of organization, and 

 not only remains chiefly fluid, but, in a large 

 number of instances, does not deposit any 

 part of its contents in a solid form until sub- 

 sequently to its removal from the living body, 

 or after the death of the patient. 



In the earliest stage of inflammation, and 

 before effusion has yet occurred, the morbid 

 appearances of the serous membranes are 

 limited to an injection, or active congestion of 

 their vessels. Most of these, it will be recol- 

 lected, are arranged as a flattened plexus in 

 the areolar tissue which forms so large a part 

 of the membrane ; and the injection of this 

 plexus, at first in isolated points, and after- 

 wards in larger patches, gives to these parrs 

 of the free surface a heightened red colour, 

 which is clearly visible through the thin and 

 almost transparent layer of cells, alone inter- 

 vening between the capillaries and the interior 

 of the membrane. But although a superficial, 

 patchy, and well-marked redness, dependent 

 on congestion of the minutest vessels, con- 

 stitutes a tolerable presumption of the presence 

 of inflammation, yet such a state can be so 

 closely imitated by conditions which are not 

 inflammatory, such as a merely passive ve- 

 nous congestion) due to position of the body, 

 mode of death, and a variety of other causes, 

 ^-as to be, in a majority of cases, of little 



value as evidence of this process. And even 

 in instances where the symptoms during life 

 have rendered the existence of inflammation 

 probable, an examination after death has often 

 detected no such appearance ; whence it would 

 seem that this vascularity is capable of dis- 

 turbance or removal, either during the phe- 

 nomena of death, or after that event has hap- 

 pened. And it is also to be noted, that the 

 different serous structures seem liable to this 

 appearance in a very different degree : some, 

 as the arachnoid, scarcely ever presenting any 

 trace of such a suffusion ; while in others, as 

 the pleura, it is much more frequent. So 

 that, on the whole, it may be stated that 

 neither does its presence affirm, nor its ab- 

 sence deny, the occurrence of inflammation ; 

 still less, where present, is its amount to 1 be 

 considered any measure of the intensity of the 

 process. 



An alteration in the texture of the mem- 

 brane itself is probably immediately subsequent 

 to this injection in the order of time, and is 

 generally seen in connection with it. Its 

 surface, instead of the smooth and shining 

 appearance which it ordinarily possesses, be- 

 comes dull and dim, while it is dry and almost 

 rough to the touch ; and at the same time the 

 thin and transparent expanse of its texture 

 acquires a milky opacity, and an increased 

 thickness, which in the more delicate serous 

 membranes is especially well marked. The 

 former of these appearances probably indicates 

 some affection of the epithelium, which clothes 

 the free surface of the membrane ; but the? 

 latter is due to the commencement of effusion. 

 This process begins where we should natu- 

 rally expect it, viz. in the immediate neigh- 

 bourhood of the vessels, or in the subserous 

 and neighbouring areolar tissue' in which they 

 ramify ; and by the filling and distention of 

 the meshes of this net-work, it gradually com- 

 municates its own appearances to the sur- 

 rounding tissue generally. 



The next stage is constituted by the ap- 

 pearance of the products of inflammation on 

 the inner or free surface of the membrane, or 

 the effusion of a plastic fluid into their cavity. 



This effusion is at first a clear transparent 

 fluid, of a tolerably limpid consistence. It is 

 true that we are rarely able to verify this 

 transparency in the exsudation of the larger 

 serous membranes ; but the condition of the 

 blood plasma from which it is derived, and the 

 similar appearance which is visible in the case 

 of fluid effused into the inflamed anterior 

 chamber of the eye, together leave no- doubt 

 of the fact. 



In a space of time which is a very short 

 one, this uniformly fluid state usually gives 

 place to a greater or less opacity and solidi- 

 fication; and in this, the earliest stage in 

 which the effusion is generally recognized, it 

 offers the appearance of a milky semifluid 

 substance, which either forms the whole of its 

 mass, or is mixed with a variable quantity of 

 serum, from which it has thus already begun 

 to separate. 



The composition of this effused fluid exhibits 

 M M 3 



