60 LIBBIE H. HYMAN 



amoebae withdrew their pseudopodia when placed in cyanide 

 solutions of the concentrations which we had been accustomed to 

 employ. This difficulty was surmounted by resorting to very 

 strong solutions of cyanide and the following procedure was 

 adopted. The amoebae were mounted on a slide in a drop of 

 water, a single, favorable specimen selected, its form, position of 

 pseudopodia, direction of movement, etc., carefully noted, and 

 then, while it was being observed under the low power, a drop 

 of strong cyanide solution was allowed to fall upon it from a 

 pipette. Movement ceases instantaneously with the pseudo- 

 podia fully extended, and in a few seconds death and disintegra- 

 tion begin. 



The potassium cyanide was weighed out fresh for each experi- 

 ment with some care but not with quantitative precautions so that 

 the concentrations as stated are only approximate. Further- 

 more, in stating the concentration employed, I have taken no 

 account of the dilution of the soltuion due to the water in which 

 the amoeba is mounted. The amoeba is therefore really ex- 

 posed to a concentration somewhat less than that which is stated. 

 In point of fact, I have made definite mention of concentration 

 only in order to give some idea of about the strength required 

 since the effect of a given solution varies greatly with the tem- 

 perature and with the amoebae themselves. The experiments de- 

 scribed below were always performed at room temperature 

 (about 21 or 22°C), as I found it impractical to work on cold 

 days of after a cold night, but even so, the variations in the 

 organisms are so considerable that one must in practice make up 

 a strong solution, say molecular, and then dilute it until the 

 desired effect is obtained. 



Observations were made with a Leitz objective no. 4 and ocular 

 no. 4. Drawings are necessarily free-hand, and hurriedly done as 

 the disintegration occurs with great rapidity. 



1. Experiments with molecular or \ molecular KNC. 1 When a 

 drop of cyanide of this strength falls upon the moving amoeba, 



7 Solutions of cyanide of this strength are of course strongly alkaline owing 

 to the slight degree of ionization of hydrocyanic acid. This condition however 

 is not objectionable because alkali alone gives a death gradient identical with 

 that in cyanide. Of course, death occurs more quickly owing to the fact that 



