PHYSICAL PROPERTIES OF TISSUES. 63 



being very thin and aqueous as the fluid of the serous membranes ; 

 and others of more consistence as the secretion of the mucous mem- 

 branes, animal oils, &c. 



The physical and chemical properties of the fluids will engage atten- 

 tion when they fall individually under consideration ; and we shall find 

 that one of them at least the blood exhibits certain phenomena 

 analogous to those of the living solid. 



The fluids have been differently classed, according to the particular 

 views that have, from time to time, prevailed in the schools. The an- 

 cients referred them all to four, blood, bile, phlegm or pituita, and 

 atrabilis ; each of which was conceived to abound in one of the four 

 ages, seasons, climates, or temperaments. Blood predominated in 

 youth, in the spring, in cold mountainous regions, and in the sanguine 

 or inflammatory temperament. Pituita or phlegm had the mastery in 

 old age, in winter, in low and moist countries, and in the lymphatic 

 temperament. Bile predominated in mature age, in summer, in hot 

 climates, and in the bilious temperament; and atrabilis was the cha- 

 racteristic of middle age, of autumn, of equatorial climes, and of the 

 melancholic temperament. This was their grand humoral system, 

 which has vanished before a better observation of facts, and more im- 

 proved methods of physical and metaphysical investigation. The 

 atrabilis was a creature of the imagination ; the pituitous condition is 

 unintelligible to us ; and the doctrine of the influence of the humours 

 on the ages, temperaments, &c., irrational. 



Subsequently, the humours were classed according to their physical 

 and chemical properties : they were divided, for instance, into liquids, 

 vapours, and gases ; into acid, alkaline, and neutral ; into thick and 

 thin; into aqueous, mucilaginous, gelatinous, and oily; into saline, oily, 

 saponaceous, mucous, albuminous, and fibrinous, &c. In more modern 

 times, endeavours have been made to arrange them according to their 

 uses in the economy into 1, recrementitial fluids, or those intended 

 to be again absorbed ; 2, excrementitial, those that have to be expelled 

 from the body; and 3, those which participate in both purposes, and 

 are hence termed excremento-recrementitial. Blumenbach 1 divided them 

 into crude humours, blood, and secreted humours, a division which has 

 been partly adopted by M. Adelon ; 2 and Chaussier, whose anatomical 

 arrangements and nomenclature have rendered him justly celebrated, 

 reckoned five classes: 1, those produced by the act of digestion, 

 chyme and chyle; 2, the circulating fluids, lymph and blood; 3, the 

 perspired fluids ; 4, the follicular ; and 5, the glandular. This arrange- 

 ment has been adopted by M. Magendie, 3 and, with slight modification, 

 is perhaps as satisfactory as any that has been proposed. All these 

 will have to engage attention under SECRETION. 



e. Physical Properties of the Tissues. 

 The tissues of the body possess the physical properties of matter in 



1 Institutiones Physiologies, Sect, ii., 4. Getting., 1798. 

 9 Physiologic de THomme, 2de edit., i. 124. Paris, 1829. 

 3 Precis Elementaire de Physiol., 2de edit., i. 20. Paris, 1825. 



