ELEMENTARY VITAL PHENOMENA 



221 



Upon strong magnification the granules of this swollen proto- 

 plasm show clearly molecular motion. That the strange Brownian 

 molecular movement does not occur in living organisms exclusively, 

 follows from the fact that all light, microscopic granules of what- 

 ever kind, when suspended in water or any other easily moving 

 liquid, show it. Among the most beautiful lifeless objects adapted 

 for this purpose and occurring in the organism are the fine crystals 

 (Fig. 87, III) in the calcareous sacs that lie in the body-cavity 

 of the frog on each side of the spinal column between the 

 transverse processes of adjacent vertebrae. If some of the white 

 substance be placed in a drop of water and examined under a 

 cover-glass with a high power of the microscope, the wonderful 

 picture of this restless, trembling dance of lifeless crystals is pre- 



FiG. 87. — Brownian moleculai- movement. /. Closterium (after Strasburger). In the vacuoles, A', 

 at the two ends of the creseent-shaped body there are numerous granules in active molecular 

 motion. //. A so-called salivary corpuscle, a dead and spherically contracted leucocyte from 

 the human saliva, in the swollen contents of which the granules are in dancing motion. 

 ///. Crystals from the calcareous sacs of the frog ; when put into water they show a 

 restless, dancing motion. 



sented in its most graceful form, especially in the smaller crystals. ^ 

 When the English botanist Brown in the year 1827 discovered 

 such peculiar motions in plant-cells, it was believed that the 

 motion of the fine granules was an active one, resulting from 

 the vibrations of their molecules, and it was accordingly termed 

 " molecular motion." In accordance with more modern ideas this 

 view became untenable, and for a long time the significance of the 

 puzzling phenomenon was not understood. But in the year 1863 

 Wiener, and soon afterwards Exner, studied very carefully the 

 physical conditions of the motion, and found an explanation that 

 is in entire accord with our present ideas of the molecular con- 

 dition of liquids. In fact, the behaviour of the molecules of a 

 liquid even requires such phenomena of motion of small light par- 



> Of. p. 4. 



