. II. MOLECULAR ATTRACTION. 29 



LECTURE II. 



MOLECULAR ATTRACTION ; CAPILLARY FORCES J IMBIBITION. 



ARGUMENT. Necessity of food for living beings. Capillary attraction, 

 imbibition, and endosmose require to be studied on account of their 

 agency in the phenomena of absorption and exhalation. Capillary at- 

 traction^ phenomena of; theory. Imbibition, phenomena of; differs for 

 different liquids and at different temperatures. Its agency important 

 in animals and plants. Hales's experiments on the imbibition of plants; 

 his results due to atmospheric pressure. The effects of chemical affinity 

 produced by capillary forces and molecular attraction ; fresh water ob- 

 tained by the filtration of salt water through sand. 



EVERY one knows that a living body requires, for its con- 

 tinued existence, the constant introduction of new sub- 

 stances into its system. These substances, the greater 

 number of which are solids, are transformed and reduced 

 to the liquid state by means of certain functions of the 

 organism. In this state they pass into particular cavities, 

 from whence, after having undergone other transformations, 

 they escape. We saw, in the first lecture, how the porosity 

 of the tissues of living beings allowed them to imbibe and 

 to become impregnated with those liquids with which they 

 came in contact. We cannot, therefore, give you a satis- 

 factory account of the phenomena of absorption and exhala- 

 tion without considering the part which is played by capil- 

 lary attraction, imbibition, and endosmose, phenomena 

 which, as we already know, can be exercised by inorganic 

 bodies. The importance of studying these two functions is 

 so great, that I purpose devoting the whole of this lecture 



