SEROUS AND SYNOVIAL MEMBRANES. 



531 



order, and of weightier influence upon its 

 termination. Here, an accompanying dropsy 

 of the areolar tissue is less frequent and 

 prominent, but it still generally follows at a 

 certain stage of duration and intensity : it is 

 usually ascribed to the pressure of the dis- 

 tended belly acting upon the vena cava, and 

 producing a secondary dropsy from the 

 branches of the systemic circulation which 

 join that vein. 



In another class of cases, the serous effu- 

 sion is still common to the areolar tissue and 

 the serous membranes, but it arises from a 

 different cause ; one which is no longer a 

 mechanical impediment, but a chemical altera- 

 tion. The dropsy of chlorosis is a good 

 example of this species of effusion, and to it 

 may probably be also referred that seen in 

 the latter stage of phthisis and other ex- 

 hausting disorders. Analysis shows, that in 

 these ancemice the blood is rendered much 

 poorer by the loss of a considerable propor- 

 tion of its albumen, and the serum of the 

 thus diluted fluid possesses a greater tendency 

 to transude the membranous walls of the 

 vessels, and pervades the surrounding struc- 

 tures in an undue quantity. Below a certain 

 percentage of albumen, Andral affirms the 

 occurrence of dropsy to be tolerably constant. 



To these two classes may be added a third, 

 in which serum is found in these structures 

 without any sign or symptom of its presence 

 having been detected during life. These 

 cases are so numerous, that, even after sub- 

 tracting a considerable number as possibly 

 due to neglect or difficulty of recognition 

 during life, a large number still remain, in 

 which the effusion may be fairly presumed to 

 have taken place after death. And in many 

 instances, they are not only affected by gravi- 

 tation, but, like the very analogous condition 

 of the areolar tissue, their occurrence seems 

 to be favoured by it. Yet, as such appear- 

 ances are absent from a large majority of 

 post-mortem inspections, it will follow, that 

 the effusion of this fluid is to be ascribed, at 

 least in part, to some conditions other than 

 mere gravity. These are probably similar to 

 the circumstances which conduce to the pro- 

 duction of the preceding class of effusions, a 

 deficiency of the albuminous constituent in 

 the blood, or, with lesser likelihood, the 

 condition of the walls of the containing 

 vessels themselves. They thus appear to be 

 due to both a mechanical and chemical affec- 

 tion of the blood, and so seem to offer an 

 union of the two causes to which the pre- 

 ceding classes have been severally ascribed. 



Many of the serous fluids which are found 

 in the ventricles of the brain and beneath its 

 arachnoid membrane, offer sufficient distinc- 

 tions in their nature and causes to merit 

 recognition as a separate variety. They are 

 alike independent of physical obstruction of 

 the vessels, or of a qualitative alteration of 

 their contents ; while their quantity, which is 

 frequently a considerable one, and the corre- 

 sponding diminution of the size of the brain, 

 together clearly indicate that they are not 



due to mere post-mortem phenomena. But 

 while, on the one hand, they are unattended 

 by these, the ordinary causes of such effu- 

 sions, and are devoid of all symptoms which 

 would indicate them as in themselves mor- 

 bid ; so, on the other, they are not present in 

 the healthy subject. Hence we may deduce, 

 first, that they are related to some abnormal 

 condition ; and secondly, that this relation is 

 not an immediate one. This may be confirmed 

 by considering that the organ bathed by these 

 fluids is one which, from its physical and 

 physiological properties, its soft consistence 

 and important functions, is both peculiarly 

 susceptible of disturbance from pressure, arid 

 ready to give signs of such disturbance ; so 

 that the absence of these indications betokens 

 a nicety of adaptation of the fluid to the 

 cranium and its contents which is hardly to 

 be explained in any other way than by sup- 

 posing that this adaptation is itself the ob- 

 ject which the presence of the serum fulfils, 

 or that the want of it is the condition which 

 necessitates the effusion, if indeed it does not 

 more immediately give rise to it. 



In the cerebro- spinal fluid itself, we are pre- 

 sented with a more normal counterpart of 

 this scarcely morbid effusion ; since a fluid of 

 similar constitution, in lesser quantity, is here 

 a constant phenomenon. In the loose and 

 vascular areolar tissue between the arachnoid 

 and the spinal cord, this perpetual dropsy is 

 the natural condition of the part;, and is 

 perhaps due to the greater mobility enjoyed 

 by the vertebral column where it surrounds 

 these parts of the nervous centre, a freedom 

 of movement which requires that they, in 

 their turn, should be more carefully protected 

 from external violence. 



Physical and chemical properties. The 

 appearances of the fluid found in the cir- 

 cumstances above mentioned are tolerably 

 uniform, and the few variations that occur 

 are chiefly of an accidental nature. It is 

 usually a limpid, colourless, and transparent 

 fluid, of a faintly alkaline reaction ; and, in a 

 state of purity, it offers no trace of organiz- 

 ation, either to the naked eye or the micro- 

 scope. In its consistence, however, it is 

 susceptible of great differences. It varies 

 from the limpidity of water to the viscidity 

 of synovia ; and when containing very much 

 albumen, is sometimes even thicker and more 

 tenacious than this liquid. Its colour is very 

 frequently and greatly affected by admixture 

 with blood, bile, and other matters ; or by 

 the partial precipitation of its albumen ; or, 

 more rarely, by the solidification or crystal- 

 lisation of fatty constituents. Many of these 

 causes also affect its transparency, giving it 

 more or less opacity, as well as colour. Its 

 alkalinity is less liable to variation ; but occa- 

 sionally it is neutral, and very rarely acid. 

 Its unorganized character is only interfered 

 with by accidental impurities similar to those 

 above noticed. 



The chemical composition of these fluids 

 is much more variable; indeed it is very pro- 

 bable that scarcely any two of them are 

 M M 2 



