TISSUES OF THE BODY. 157 



Of all these components inucin alone requires further consideration. 

 It appears in mucus under two forms : as an insoluble substance, merely 

 gelatinising in water, and which remains behind on a filter } and as a 

 soluble matter which may be filtered, Now, in that the reactions of both 

 are the same, we are warranted in supposing that mucin in a pure state 

 is insoluble, and has probably acquired its solubility by admixture with 

 other compounds, especially alkalies, an hypothesis which appears to 

 receive further support from its parallelism with many protein matters in 

 this respect. 



Synovia also reminds us of mucus (FrericJis). We meet it as a clear, 

 colourless, or straw-coloured fluid of slimy consistence and alkaline re- 

 action, in which the microscope reveals to us the epithelial cells of the 

 capsule of the joint, which have been shed, as well as lymphoid cor- 

 puscles. The use of this liquid is, as is well known, to retain the parts 

 entering into the formation of the joint in a moist and slippery 

 condition. 



Synovia, strangely enough, has farther the same constituents as mucus, 

 in addition to which albumen is also present. Of salts we find, chloride 

 of sodium, basic phosphates of the alkalies, sulphates of the alkalies, phos- 

 phatic earths, and carbonate of calcium. 



The two following analyses of Frericlis may serve as an example of its 

 composition per cent. The first applies to the synovia of an ox fed in 

 the stall, while the second is that of one in pasture : 



II. 



Water, 969-90 948-54 



Solid constituents, . . . 30' 10 51*46 



Mucus with epithelium, . . 2 -40 5 -60 



Albumen and extractives, ... 15 '76 35 '12 



Fats, 0-62 0-76 



Salts, .... 11-32 9-98 



According to this, it would appear as though the friction of the surfaces 

 of the joints induced by exercise .were of importance in the formation of 

 synovia, for we find it during inactivity, watery, less viscid, and poorer in 

 mucin. At the same time, however, its quantity is far more consider- 

 able. Again, on energetic bodily exertion the quantity of this fluid 

 decreases considerably, and the amount of mucin increases, with its 

 oiliness or thickness. The contents of bursae and the sheaths of ten- 

 dons appear, also, according to Virchow, to be allied to synovia in com- 

 position. 



Now, as to the formation of mucus and the origin of mucin parti- 

 cularly, the older views, which referred both exclusively to the secretion 

 of special glandular organs, the so-called mucous glands, can no longer 

 obtain, in that the proportion of the fluid stands in no relation to the 

 frequency or rarity of those glands ; and in that synovial capsules, which 

 have none of the latter, nevertheless secrete mucus. Epithelial cells, 

 however, appear to stand in close relation to the origin of mucin, beside 

 which the elements of the glands themselves, without doubt, play a part 

 in the formation of mucus. There seems, indeed, much probability in 

 the supposition, that an alkaline fluid transuding through the capillaries 

 of mucous membranes macerates the cast-off cells 3 aided by the natural 



