82 PHYSIOLOGY OF STREAMING MOVEMENTS 



preparation of the frog's gastrocnemius to respond to an electrical excitation 

 by a prolonged contraction instead of by a simple twitch. Curare paralyses 

 the motor nerve-endings in muscle, and hence renders the latter irrespon- 

 sive to nervous excitation. Muscarin (0-5 per cent.) excites the inhibitory 

 nervous mechanism of the frog's heart, and so decreases its excitability 

 that it ceases to beat, while Atropin (0-5 per cent.) paralyses the inhibitory 

 mechanism, and hence causes the beat to recommence. 



Muscarin. If a drop of 2 per cent. Muscarin is placed upon a cell 

 of Nitella streaming almost immediately ceases, and recommences within 

 five minutes if a drop of 2, per cent. Atropin is added. If the Muscarin 

 is washed away as soon as streaming has ceased, it recommences in a few 

 seconds to a minute, and is active in two to three minutes. Recovery 

 also occurs even if the Muscarin is not removed, and no Atropin added ; 

 streaming recommencing in five to ten minutes, and being fairly active 

 in fifteen to twenty. 



The temporary stoppage is therefore due to a shock-effect, and if the 

 Muscarin is allowed to diffuse in slowly, none is produced. Moreover, 

 if the shock-stoppage and recommencement in water are repeated from 

 one to a few times, streaming may become more rapid, and may no 

 longer be stopped by sudden immersal in 2 per cent. Muscarin, although 

 after prolonged immersal it undergoes progressive retardation. Suddenly 

 replacing the Muscarin solution by water may cause a similar temporary 

 stoppage, and hence the latter is due more to sudden changes in the 

 concentration of the external medium than to any poisonous effect of 

 the Muscarin. 



Sudden immersal in dilute solutions will produce a similar effect, 

 and, in fact, i and 2' per cent, solutions of sodium chloride are nearly 

 as poisonous to Nitella as are similar solutions of Muscarin (i and 2 grams 

 in 100 cc.). Thus if a few cells of Nitella are placed in from 30 to 35 cc. 

 of 0-5 per cent. Muscarin, they continue to show active streaming for 

 several days. In i per cent, solution streaming slows, and permanently 

 ceases on the second to fourth day as the cells die. In 2 per cent, 

 solutions slow streaming may still be shown after six to twelve hours, 

 but death ensues on the first or second day 1 . Closely similar results were 

 yielded by Char a fragilis and Chara foetida. 



The shock- stoppage is less readily induced in the case of Elodea 

 and Vallisneria, although in 2 per cent, solutions streaming usually 

 ceases in a few hours, death following after twelve to forty-eight hours. 



1 The plants must be gradually accommodated to the solution, for if Nitella is suddenly 

 immersed in 2 per cent. Muscarin the first stoppage and recommencement may be followed within 

 an hour either by progressive retardation, or irregular fluctuations leading ultimately to a permanent 

 stoppage. The plant is apparently unable to accommodate itself to so sudden and violent a dis- 

 turbance of equilibrium. 



