252 FRANCIS DARWTN. 



the filament subsequently showed itself to be still alive by- 

 changing its form and contracting with dilute acetic acid. This 

 filament was therefore made to partially contract without being 

 killed, instead of the normal effect of the poison being produced, 

 viz. death without contraction. After numerous trials 1 conclude 

 that irrigation with acid of this strength either causes complete 

 or almost complete contraction, or else no efTect is produced and 

 the filament withstands the poison. This is a remarkable fact, 

 as the glands are soon killed and blackened by \ per cent, osmic 

 acid; it shows that i\\e filaments, when once protruded, are inde- 

 pendent of the life of the gland. With 1 per cent, osmic acid I 

 succeeded in obtaining a different result; a filament began to 

 contract and then died in a partially expanded state, and after- 

 wards resisted the action of strong acetic acid. In another 

 instance the filament was half poisoned by osmic acid and only 

 contracted after prolonged irrigation with 20 per cent, acetic acid. 

 In another case a filament contracted partially with osmic acid and 

 then withstood 20 per cent, acetic acid, showing that it was killed 

 by the osmic acid. 



Various salts. — Carbonate of ammonia in di\[\3iie solutions, viz. : 

 I per cent., causes moniliform contraction ; the filament becomes 

 partially concentrated into a ball, and then recovers, and extends 

 itself again. The most interesting points in connection with this 

 salt have no bearing on the simple contraction of the filaments, 

 and will be discussed later. The same remark applies to the 

 carbonates of potassium and sodium, both of which cause con- 

 traction in I per cent, solutions. 



Chloride of gold in \ per cent, solution causes rather languid 

 contraction. But the filaments are killed by it, and become 

 transformed into soap-bubble masses. 



Nitrate of silver in \ per cent, solution has the same effect, 

 viz. contraction and death, followed by the production of a soap- 

 bubble mass. 



Iodine. — A solution (Schacht's) composed of iodine 2 grains, 

 iodide of potassium 6 grains, water 2 ounces, was employed. 

 Violent moniliform contraction is produced, and the rounded 

 mass into which the filament is transformed by contraction is 

 stained yellow. In one instance the contracted mass consisted of 

 two parts, a heap of transparent soap-bubbles and a yellow mass. 

 There can be little doubt that the iodine and not the iodide of 

 potassium is physiologically active in this solution. When 

 diluted so that the iodine is about in the proportion ^ per cent., 

 the solution is not poisonous, or only slightly so. It is known to 

 have stimulating but not poisonous effects on germinating seeds.^ 



Alcohol. — Strong contraction is produced by irrigating with a 

 1 Heckel, ' Comptes rendus/ 1875, p. 1170. 



