ON PROTRUSION OF PROTOPLASMIC FILAMENTS. 259 



The important result derived from these experiments is that, 

 although there is most remarkable variability in the temperatures 

 at which contraction took place, yet no filament withstood 

 without contraction a temperature of more than 57° C. No in- 

 creased activity was observed at lower temperatures. 



The following experiments were made with Sachs' heating 

 box : 



Experiment 7. 



Filament extended. 



Filament contracted. The microscope was 

 then removed, another specimen mounted 

 and then replaced. 

 Filament extended. 

 Filament contracted. 



Experiment 8. 



Filament extended. 



i> 



Filament contracted ; microscope removed 

 and replaced. Fresh filament observed. 



Fresh filament contracted. Microscope re- 

 moved and new filament (3rd) observed. 



Filament contracted. 



The average temperature of contraction from the experiments 

 with Sachs' box is 45"4°, the average for the .series with Velten's 

 apparatus being 3 8' 7°, the average of the whole of both series 

 being 42° C. 



Electrical stimulation. — By using a modification^ of the elec- 

 trodes usually employed in microscopical work the filaments 

 were easily subjected to the influence of the induced current. 

 Clear and unmistakeable contraction was thus produced, and the 

 ob.servation was several times repeated. No contraction was 

 produced until the current was approaching the strength at 

 which water is decomposed. The filaments were not thrown into 

 a state of activity by weaker currents ; and this agrees with 

 Heidenhain's observations on the hairs of Tradescautia (quoted 

 by Sachs, 'Physiologic Vegetale,' p. 85). He found that weak 

 currents produced no effect on the protoplasm, while strong 

 currents rapidly stopped all movement. On the other hand, 

 Briicke and Max Schultze (qnoted in Sachs, ' Phys. Veg.', p. 86) 



' I succeeded so easily with this modified arrangement, when I failed 

 with the ordinary form of microscopic electrodes, that it seems worth 

 describing. I am indebted for tiie suggestion to Prof. E. Ray Lankester. 

 He pointed out thai the object to be examined might be placed in a drop of 

 water hanging from the under surface of a thiu glass cover, just as in the 

 gas-chamber. One electrode is fixed to the uuder surface of the thin glass, 

 the other is movable and is brought cautiously into the field of vision until 

 it closely approaches the object. This arrangement is shown in the accom- 

 panying woodcut, which gives the iuslrumeul iu section. 



