CHARACTERISTICS OF PROTOPLASM 5 



vegetable circulation, whereas the movement of the protoplasm round the 

 interior of the cell is called rotation. 



The first account of the movement of protoplasm was given by Rosel in 

 1755, as occurring in a small Proteus, probably a large fresh-water ameba. 

 His description was followed twenty years later by Corti's demonstration of 

 the rotation of the cell sap in characeae, and in the earlier part of the last 

 century by Meyer in Vallisneria, 1827; Robert Brown, 1831, in "Staminal 

 Hairs of Tradescantia." Then came Dujardin's description of the granular 

 streaming in the pseudopodia of Rhizopods and movements in other cells of 

 animal protoplasm (Planarian eggs, von Siebold, 1841; colorless blood 

 corpuscles, Wharton Jones, 1846). 



The Power of Response to Stimuli, or Irritability. Although the move- 

 ments of the ameba have been described above as spontaneous, yet they 

 may be increased under the action of external agencies which excite them 

 and are therefore called stimuli. If the movement has ceased for the time, 

 as is the case if the temperature is lowered beyond a certain point, move- 

 ment may be set up again by raising the temperature. Contact with foreign 



FIG. 5. Cell of Tradescantia Drawn at Successive Intervals of Two Minutes. The 

 cell contents consist of a central mass connected by many irregular processes to a peripheral 

 film, the whole forming a vacuolated mass of protoplasm, which is continually changing 

 its shape. (Schofield.) 



bodies, gentle pressure, certain salts, and electricity produce or increase the 

 movement in the ameba. The protoplasm is, therefore, sensitive or irritable 

 to stimuli, and shows its irritability by movement or contraction of its mass. 

 The effects of some of these stimuli may be thus further detailed: 



a. Changes of Temperature. Moderate heat acts as a stimulant; the 

 movement stops below o C. (32 F.), and above 40 C. (104 F.); between 

 these two points the movements increase in activity; the optimum tempera- 

 ture is about 37 to 38 C. Exposure to a temperature even below o C. 

 stops the movement of protoplasm, but does not prevent its reappearance if 

 the temperature is raised; on the other hand, prolonged exposure to a tem- 

 perature of over 40 C. kills the protoplasm and causes it to enter into a 

 condition of coagulation or heat rigor. 



b. Mechanical Stimuli. When gently squeezed between a cover and 



