PROPERTIES OF ANIMAL BODIES. 99 



same power ; yet the motion of one is insensible to the eye, 

 while that of the other is distinctly visible. 



22. {By means of the alterative powers, all the changes 

 which take place in the composition of the solids and fluids 

 of the body are effected. By these, the food is changed into 

 chyme, and then into chyle ; chyle into blood, and blood into 

 bone, muscle, cartilage, &c. By these, animal heat is pre- 

 served uniform ; and the solids preserve their cohesion, and 

 the fluids their fluidity} In short, it is these powers that 

 for a time successfully resist the agency of chemical laws. 



23. Some physiologists attempt to account for every thing 

 that takes place in the body, on chemical or mechanical 

 principles. But the vital laws, or organic forces, form com- 

 pounds which could never be produced by chemical affinity. 

 In fact, they are antagonistic forces, fighting against each 

 other. The chemist can decompose blood, bile, saliva, al- 

 bumen, gelatine, and fibrin, but he can not re-form one of 

 them. He can no more make a piece of bone, than he can 

 make a diamond. 



24. The physical properties of the animal tissues are 

 usually reckoned as five in number, viz.^elasticity, extensibil- 

 ity, flexibility, imbibition, and evaporation.} 



25. f Elasticity is one of the physical properties of animal 

 matter. It is that power which tends to restore parts that 

 have been stretched OF extended to their former state. It is 

 possessed in the greatest degree by the cellular tissue, which 

 enters largely into the composition of all the structures in 

 the body. All the organs and membranes of the body are 

 in a constant state of extension. All the hollow organs, as 

 the stomach, gall-bladder, and blood-vessels are kept distend- 

 ed by the volume of their contents. The extensor and 

 flexor muscles, when in a state of inaction, are in a state of 

 extension. If such were not the case, all the organs would 

 contract and shrink to a comparatively small size) 



26. (When the stomach is empty, its sides contract till 

 jy almost touch each other. When a muscle is cut, the 



