LIVING ORGANISMS 21 



particles, possibly of irregular form, and that 

 water fills up the spaces between such particles. 

 Such molecules are assumed to be in a state 

 of incessant movement, and these movements 

 are associated with the absorption and libera- 

 tion of water. A watery consistence is 

 essential to the phenomena of life. Move- 

 ments of minute particles of matter in a 

 fluid are well illustrated by the Brownian 

 movements seen under the microscope, magni- 

 fying say 250 diameters, if we squeeze and 

 examine a little bit of fresh vegetable tissue. 

 The minute particles are seen to be in a state 

 of incessant vibration. 



9. Chemical composition. Of the seventy 

 elements known to chemists only from eighteen 

 to twenty have been found in living matter, 

 and of these the chief are oxygen, hydrogen, 

 nitrogen and carbon. With these are asso- 

 ciated, of the non-metals, sulphur, phosphorus, 

 and chlorine ; of the alkalies, sodium and 

 potassium; of the alkaline earths, calcium 

 and magnesium ; and of the metals only one, 

 iron. Minute quantities of other substances 

 have been found, such as argon, silicon, 



