BY CAPILLARY ATTRACTION. 5 



necessary in order to cause water to flow out of 



moist wood. We may form some idea of the force Prodigious 



with which porous organic substances, such as dry 



wood, absorb and retain water, if we remember, that 



by inserting of wedges of dry wood in proper cuts, water * 



and subsequently moistening them, rocks may be 



split and fractured. 



When we compare with the properties just enu- 

 merated, which belong to all porous bodies, those 

 properties which are observed in animal substances 

 under the same circumstances, it appears plainly, 

 that these animal substances have pores in certain Animal tis- 

 directions, although these openings are so minute porous! 

 that they are not, in the case of most tissues, per- 

 ceptible even with the aid of the best microscopes. 



It has been mentioned that tendons, ligaments, Amount of 

 cartilages, &c., contain, in the fresh state, a certain peiied by 

 amount of water, which, according to all experi- fom tis- 

 ments made on the subject, is invariable ; and that 

 several of their properties depend on the presence 

 of this water. (CHEVREUL.) When these sub- 

 stances, wrapped in bibulous paper, are subjected 

 to a powerful pressure, a certain proportion of this 

 water is expelled. Fresh and flexible vessels lose in 

 this way 37*6 per cent., and the yellow ligaments of 

 the vertebrae lose 35 per cent, of water. This pro- 

 perty, namely, that of losing water under pressure, 

 is only found in porous substances. It is obvious 

 that by pressure, that is, by diminution of the size 

 of the pores, only that portion of water can be 

 pressed out which is not retained by chemical 



