ABSORPTION OF FATS AND INSOLUBLE SUBSTANCES. 317 



have shown the facility with which liquids may be absorbed from the lungs and the air- 

 passages, but it must be remembered that the natural conditions are never such as to ad- 

 mit of this action. The normal function of the lungs is to absorb oxygen and sometimes 

 a little nitrogen from the air ; and the absorption of any thing else by these surfaces is 

 unnatural and generally deleterious. 



Absorption from Closed Cavities, Reservoirs of Glands, etc. Facts in pathology show- 

 ing absorption from closed cavities, the areolar tissue, the muscular and nervous tissue, 

 the conjunctiva, and other parts, are sufficiently numerous. In all cases of effusion of 

 serum into the pleural, peritoneal, pericardial, or synovial cavities, in which recovery 

 takes place, the liquid becomes absorbed. It has been shown by experiment that warm 

 water injected into these cavities is disposed of in the same way. Eifusions into the 

 areolar tissue are generally removed by absorption. In cases of penetration of air into 

 the pleura or the general areolar tissue, absorption likewise takes place ; showing that 

 gases may be taken up in this way as well as liquids. Effusions of blood beneath the 

 skin or the conjunctiva or in the muscular or nervous tissue may become entirely or in 

 part absorbed. It is true that these are pathological conditions, but, in the closed cavi- 

 ties, the processes of exhalation and absorption are constantly going on, although not 

 very actively. As regards absorption from the areolar tissue, the administration of 

 remedies by the hypodermic method, which is now so common, is a familiar proof of the 

 facility with which soluble principles are taken into the blood when introduced beneath 

 the skin. 



Under some circumstances, absorption takes place from the reservoirs of the various 

 glands, the watery portions of the secretions being generally taken up, leaving the solid 

 and the organic matters. It is supposed that the bile becomes somewhat inspissated 

 when it has remained for a time in the gall-bladder, even when the natural flow of the se- 

 cretion is not interrupted. Certainly, when the duct is in any way obstructed, absorption 

 of a portion of the bile takes place, as is proven by coloration of the conjunctiva and 

 even of the general surface. The serum of the blood, under these conditions, is always 

 strongly colored with bile. 



It is probable that some of the watery portions of the urine are reabsorbed by the 

 mucous membrane of the urinary bladder, when the urine has been long confined in its 

 cavity, although this resorption is ordinarily very slight. A great many cases of dis- 

 charge of urinary matters by the stomach and intestines, skin, etc., when the urine has 

 been long retained, have been reported by the older physiologists and were supposed to 

 indicate resorption of these principles from the bladder. The mechanism of the excretion 

 of urinary matters was not understood before the experiments of Prevost and Dumas, 

 who showed that urea accumulates in the blood after the extirpation of both kidneys 

 in the inferior animals. It is now generally admitted that this takes place when the 

 function of excretion of urine is seriously interfered with, and that an attempt is made 

 by Nature to remove these effete principles from the system by the stomach, intestine, 

 skin, and lungs. It is possible, therefore, that the vicarious discharge of urinary matters, 

 in the cases reported before the true process of excretion by the kidneys was understood, 

 was due to accumulation of the constituents of the urine in the blood, and not to their 

 resorption from the urinary passages. 



Absorption may take place from the ducts and the parenchyma of glands, although 

 this occurs chiefly when foreign substances have been injected into these parts. 



Absorption of Fats and Insoluble Substances. 



The general proposition that all substances capable of being absorbed are soluble in 

 water or in the digestive fluids must be modified in the case of the fats. These are never 

 dissolved in any appreciable quantity in digestion, the only change which they undergo 

 being a minute subdivision in the form of a very fine emulsion. In this condition, the 



