LIVING AND NON-LIVING PARTICLES. 189 



meant by a particle of living matter, it will be well to con- 

 sider in this place what may be learnt by comparing very 

 minute lifeless particles with very minute living particles 

 under very high magnifying powers. 



A little inorganic matter of any kind, but in a state of 

 very minute subdivision may be subjected to examination. 

 Take for example a little of the deposit of phosphate of 

 lime which has been precipitated from a solution of a salt 

 of lime by the addition of a soluble salt of phosphoric acid. 

 What is observed when such a fine precipitate is placed 

 under the microscope ? Only a number of minute granules 

 or dots possessing no definite form and exhibiting no indica- 

 tions of structure. If the deposit be examined by the 

 highest powers at our command, the apparent size of the 

 particles will indeed be increased, and others which were 

 previously invisible, will be brought into view, but no 

 appearance of structure can be recognised. Spots they 

 appeared under moderately high powers, and mere spots 

 they remain under the highest magnifying powers we can 

 at this time obtain. Certain movements are, however, to be 

 observed. Each little particle revolves and oscillates in the 

 fluid about the adjacent particles. These movements have 

 been termed molecular, and were first described many years 

 ago by Robert Brown. We know that the particles under 

 observation are inorganic, and we are therefore quite sure 

 that the movements we witness are physical. 



Next let us take a small fragment of dead animal or 

 vegetable matter, and place it in a few drops of pure water 

 on a glass slide, and examine carefully the clear fluid under 

 the microscope. The water appears as transparent and 

 structureless as the glass on which it rests. The two slides, 



