STIMULI AND THEIR ACTIONS 393 



well as leucocytes of various species of animals, behave in all respects 

 analogously; and even the protoplasmic streaming of plant-cells 

 shows the same phenomena. Max Schultze ('63) and Nageli ('60) 

 measured the rate of granular streaming in the protoplasmic 

 threads of the cells of Tradescantia and AHtella with increasing 

 temperature, and saw how it became constantly greater; and 

 Ktihne (I.e.) found that the protoplasm of the cells of the stamen- 

 hairs of Tradescantia at a temperature of 45° C. exhibits powerful 

 contractile phenomena, becoming collected into globules in the 

 typical manner (Cf. Fig. 35, p. 95). 



In the exciting effect of rising temperature upon protoplasmic 

 motion an important fact is to be noticed, which is of great 

 importance in the explanation of many phenomena to be treated 

 later. This is the fact that the two phases of the motion, that of 

 expansion and that of contraction, are not equally excited.^ This 

 can be established best in marine Ehizopoda that possess long, 

 thread-like pseudopodia, in which the protoplasmic particles have 

 to pass over a very long path. -E.g., in the action of rising 

 temperature upon Bhizoplasma (Fig. 130, p. 285) it is seen that up 

 to about 31° — 32° C. both phases are gradually excited, so that 

 the protoplasmic motion is accelerated ; but expansion outweighs 

 contraction, so that the pseudopodia extend farther and farther 

 and become more numerous. At about 31° — 32° C, the two phases 

 are equally excited. If the temperature be still more increased, 

 contraction more and more outweighs expansion, and with a very 

 slow increase of temperature up to about 39° and 40° C the 

 pseudopodia finally become completely retracted. Hence the 

 curves of excitation of expansion and of contraction do not 

 coincide, but have their maxima at different places. Without 

 doubt a similar condition is to be observed in other contractile 

 objects and with other stimuli, and it would be a very fruitful 

 task to make further studies in this direction. 



Ciliary motion is likewise gradually augmented by increasing 

 temperature up to a certain degree, as Engelmann ('79, 1) 

 has observed in ciliated epithelia, and Rossbach ("71) in 

 Infusoria. The oral mucous membrane of the frog is a con- 

 venient object for the observation of the ciliary motion of an 

 epithelium. It is easy to loosen from the palate and cut off a 

 piece of this ciliated membrane a centimetre square, the ciliary 

 motion of which is directed toward the oesophagus. If we 

 stretch such a piece with four needles upon a cork frame (Fig. 182) 

 and cover it with a cover-glass, we can observe the ciliary motion 

 for days, if the object be protected from drying, and study its rate, 

 either directly under the microscope, or by the passage of blood- 

 clots or particles of coal-dust laid upon it. In such a preparation 

 it is easy to determine that the rate and energy of the motion 

 1 Cf. Verworn ('96, 2, 3). 



