SYNOVIA is that fluid which exists within the membrane lining joints, to assist motion by lubrication ; as also in the bursa;. The membranes generally, which line the various cavities of the body, are lubricated by fluid. This varies in character according to circum stances; and among these perhaps none more tend to the requirement of especial conditions than that of active and frequent motion, in volving friction of the surfaces so lubricated.
Thus we find that the fluid of the peri cardium differs essentially from that of the ventricles of the brain ; while again the synovia, supplying moisture to the joints, varies greatly from the fluid of the pericardium, probably in order to assist the opposed surfaces in bearing friction in an exaggerated degree. The word attrition appears, indeed, the most appropriate to the conditions relieved by the presence of synovia, placed as it is between surfaces oc casionally strongly approximated either by superincumbent weight or muscular contrac tion.
Synovia was chemically examined by Mar gueron.# The specimen he analysed was viscid, and became gelatinous soon after it was obtained. It then deposited a fibrous matter, and became clear above. Though the analysis of Margueron was not conducted on the more exact principles characterising those of the present day, it still serves to show that the specimen was peculiar as an animal fluid, and differed in one respect from the fluids generally, which lubricate surfaces. Thus it appears that as much as 11'86 per cent. was composed of fibrinous matter (fibrin), which coagulated, as stated before, soon .after the fluid was obtained.
Margueron's analysis is as follows : — It will be seen that these two analyses vary greatly — they were not made, it must be recollected, at the same date; and the methods of animal analysis are greatly improved since Margueron published. There is, however, an important point in which both analyses agree, viz. in stating phosphate of lime among the constituents of the fluid. John makes no mention of the existence of a coagulable fibrin ous matter ; a fact of much importance, which it appears desirable carefully to inquire into, insomuch as it is very possible the analyst may have extracted the synovia after coagulation had occurred within the membrane, and so obtained the clear fluid only ; while Mar gueron may have been fortunate enough to secure it before such change had taken place, and in its natural condition.
With regard to this subject, on which our knowledge is but scanty, it appears still of importance to reflect on the material before us ; and it is matter of no small interest to consider how far the results of peculiar me chanical conditions are modified by variations in the character of lubricating fluids, know ing, as we do, that, while the ventricles of the brain, subject to agitation only, contain no albumen in their lubricating fluid, the liquor of the pericardium contains that principle in abundance ; and that in the synovial fluid adapted to the lubrication of the joints, we have, in addition to albumen, not only a con siderable proportion of phosphate of lime, but probably fibrin also, as a necessary consti tuent. (G. Owen Rees.)
TASTE.—The sense by which we distin guish the sapid properties of bodies. The term, as commonly understood, includes much more than this ; being usually employed to desig nate the whole of that knowledge of the qualities of a body (except such as is purely tactile), which we derive through the sensory apparatus situated within the mouth. But it will be hereafter shown that a considerable part of this is dependent upon the assist ance of the olfactive sense; which is affected, through the posterior nares, by the odorous emanations of all such bodies as are capable of giving them off; and the indications of which are so combined with those of the true gustative sense, as to make an apparently single impression upon the sensoriuw. More over, there are certain sensorial impressions received through the organ of taste, which are so nearly allied in their character to those of touch, as to render it difficult to specify any fundamental difference between them : such are the pungent sensations produced by mus tard, pepper, the essential oils, &c. ; all of which substances produce a sensation when applied for a sufficient length of time to any part of the cutaneous surface, which can scarcely be distinguished from that excited through the organ of taste, in any other way than by its inferior intensity, and by the ab sence of the concurrent odorous emanations. The taste of such substances might, perhaps, be considered, therefore, as the composite re suit of the impressions made upon the senso rium through a refined and acute touch, and by the effect of their odorous emanations upon the organ of smell. After making full allow ance, however, for all such as can be thus ac counted for, there remains a large class of pure sapors, of which we take cognizance without the assistance of smell, and which are alto gether dissimilar to any tactile impressions : such are the bitter of quinine, the sour of tar taric acid, the sweet of sugar, the saline of common salt, (Sec. The smell can give us no assistance in distinguishing small particles of these bodies, since they are either entirely inodorous, or so nearly so as only to be recognizable through its means when in large masses ; and the most refined touch cannot afford any indication of that kind of difference among them, of which we are at once rendered cognizant by taste. Still the gustative sensa tions scarcely differ more from the tactile than some of these last differ among each other,— the sense of heat and cold, for example, from the simple sense of contact or resistance ; and we shall find that the analogy between these two senses is so strong, both as to the con ditions under which they are respectively ex ercised, and the structure of the apparatus through which the impressions are received, that they must be regarded as much more nearly related to each other than either of them is to the other senses, or than the latter are amongst themselves.