TRANSUDATION THROUGH ANIMAL TISSUES. 365 



reaction with litmus. The acid in this case passes through the wall of 

 the intestine against the pressure of the current, which is of course 

 directed from within outward. 



Endosmosis is also regulated, to a great degree, by temperature. 

 As a rule it is more active when the temperature is moderately 

 elevated. Dutrochet found that an endosmometer, containing a solu- 

 tion of gum, absorbed only one volume of water at a temperature of 

 0, but absorbed three volumes at about 34. Variations of tempera- 

 ture will sometimes even change the direction of the endosmosis alto- 

 gether, particularly with dilute solutions of hydrochloric acid. In the 

 experiments of Dutrochet, when the endosmometer was filled with dilute 

 hydrochloric acid and placed in distilled water at the temperature of 

 10, endosmosis took place from the acid to the water, if the density of 

 the acid solution were less than 1.020 ; but from the water to the acid, 

 if its density were greater than this. On the other hand, at the tem- 

 perature of 22, the current was from within outward when the density 

 of the said solution was below 1.003, and from without inward when it 

 was above that point. 



Absorption and Transudation in the Tissues of the Living Body. 

 In the experiments above detailed, performed with membranes and tis- 

 sues taken from the dead body, by which the phenomena of endosmosis 

 and exosmosis were first studied, the phenomena represent imperfectly 

 those which take place in the living organism. The property, belong- 

 ing to an animal membrane, of determining the absorption or transu- 

 dation of various liquids, depends upon its organic constitution and is 

 exercised in the greatest intensity during life. In the living body, all 

 the conditions requisite for the acts of endosmosis and exosmosis are 

 present in a higher degree than is possible in any artificial experiment. 

 The membranes and tissues are all perfectly fresh, and unaltered by 

 either desiccation or putrescence; the extent of absorbing surface is 

 indefinitely multiplied by the repeated ramification of the capillary 

 bloodvessels or the glandular tubes; the internal temperature of the 

 body is maintained at a point most favorable for the activity of endos- 

 mosis ; and finally the continuous movement of the blood and the lymph, 

 in theii respective vessels, supplies the ingredients for a constant renewal 

 of the process and at the same time removes the accumulation of the 

 transuded material. 



In the living body, accordingly, the transudation of fluids is accom- 

 plished with great rapidity. It has been shown by Gosselin, that if a 

 watery solution of potassium iodide be dropped upon the cornea of a 

 living rabbit, the iodine passes into the cornea, aqueous humor, iris, 

 lens, sclerotic and vitreous body, in the course of eleven minutes ; and 

 that it will penetrate through the cornea into the aqueous humor in 

 three minutes, and into the substance of the cornea in a minute and a 

 half. In these experiments it is evident that the iodine actually passes 

 into the deeper portions of the eye by simple endosmosis, and is not 



