TRANSUDATIONS. 309 



which a change has already commenced. These translations 

 include all those fluids which are normally or abnormally effused 

 from the blood-vessels (without laceration) into the parenchyma 

 of organs, or into enclosed or open cavities, or even on the surface 

 of the animal body. Hence we include amongst the transudations 

 the normal secretions of the serous membranes, and not merely 

 those of the lining membrane of the cerebral ventricles, of the 

 pericardium, the pleura, and the peritoneum, but also the tears, 

 the aqueous humor of the eye and the liquor amnii, and especially 

 the parenchymatous fluid or juice which moistens and nourishes the 

 tissues ; if these transudations are excessive, they form the albu- 

 minous and fibrinous exudations of pathologists. Although pa- 

 thological transudations are now frequently submitted to chemical 

 investigation, and have been more accurately analysed than the 

 normal transudations, in consequence of the greater quantity in 

 which they accumulate, we regard it as most expedient to follow 

 the purely physiological view regarding the escape of these fluids 

 from the capillaries, lest we should lose ourselves in the labyrinths 

 of pathological systems and pathological fictions ; for the assump- 

 tion of watery and serous transudations, of croupous and fibrinous, 

 and again, of serous and albuminous, can find no support either in 

 physical or chemical physiology. We have already seen, when 

 treating of the lymph (a subject closely allied, in more points than 

 one, to that we are now discussing), that in accordance with the 

 views of the most eminent physiologists of the present day, we 

 must consider the escape of water and certain constituents of the 

 liquor sanguinis through the walls of the capillaries as the result of 

 a physical necessity consequent on the penetrability of the walls of 

 the capillaries, the rapidity of the motion of the blood in them, and 

 the physical and chemical characters of the circulating fluid itself. 

 This variety in the conditions affords at the same time an explana- 

 tion of the differences in the physical and chemical properties of 

 normal as well as of excessive transudations, and of the uncertainty 

 of those attempts at classifying them, which are based either on 

 their incidental properties, or on the form of the metamorphoses 

 which they are more or less inclined to undergo. Hence, without 

 attempting any system of classification, we will proceed to notice 

 their ordinary physical characters, and their essential and incidental 

 constituents. 



The normal as well as the excessive transudations have in 

 general the same properties as the intercellular fluid or the serum 

 of the blood; they are colourless, transparent, of a sickly and 



