PEEFACE. 



THE present little work contains a series of experiments the object of 

 which is to ascertain the law according to which the mixture of two liquids, 

 separated by a membrane, takes place. The reader will, I trust, perceive 

 in these researches an effort to attain, experimentally, to a more exact 

 expression of the conditions under which the apparatus of the circulation 

 acquires all the properties of an apparatus of absorption. 



In the course of this investigation, the more intimate study of the 

 phenomena of Endosmosis impressed on me the conviction that, in the 

 organism of many classes of animals, causes of the motion of the juices 

 were in operation, far more powerful than that to which the name of Endos- 

 mosis has been given. 



The passage of the digested food through the membranes of the intes- 

 tinal canal, and its entrance into the blood ; the passage of the nutrient 

 fluid outwards from the blood vessels, and its motion towards the parts 

 where its constituents acquire vital properties, these two fundamental 

 phenomena of organic life cannot be explained by a simple law of mixture. 



The Experiments described in the following pages will, perhaps, be found 

 to justify the conviction that these organic movements depend on the 

 transpiration and on the atmospheric pressure. 



The importance of the transpiration for the normal vital process has, 

 indeed, been acknowledged by physicians ever since Medicine had an 

 existence ; but the law of the dependance of the state of health on the 

 quality of the atmosphere, on its barometric pressure, and its hygrometric 

 condition, has been hitherto but little investigated. 



By the researches contained in my examination of the constituents of 

 the juice of flesh, as well as by those described in the present work, the 

 completion of the second part of my Animal Chemistry has been delayed ; 

 but I did not consider myself justified in continuing that work until I had 

 examined the questions suggested by, and connected with those researches, 



DR. JUSTUS LIEBIG. 



, February, 1852. 



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