536 ASA A. SCHAEFFER 



conclusions would be different from what they are if all the experi- 

 ments in this paper, for instance, had been performed on amebas 

 of the granular type, or of the raptorial type, exclusively. Un- 

 fortunately, however, it is impossible at this time to give a more 

 accurate description of the amebas I used than is given above. 



The needles used in manipulating the test substances were of 

 steel and of glass. Those made of glass were superior to those 

 of steel because of their greater elasticity and resistance to clean- 

 ing agents. The glass needles were made by drawing out thin- 

 walled test tubes to a point. The diameter of the needle half a 

 millimeter back from the point was one or two microns. Occa- 

 sionally needles can be made having thinner points, so thin in 

 fact that they wave about in the water. Such needles were used 

 in the 'tickling' experiments. The most delicate mechanical 

 stimuli could be administered by means of them. The needles 

 were frequently freed from colloidal materials which readily col- 

 lect on them while working with them in the culture fluid, by im- 

 mersing them alternately in sulphuric acid and a strong solution 

 of sodium hydroxide, a number of times, and then washing in 

 distilled water and finally in ether. It was assumed that they 

 were sufficiently cleaned in this way to prevent contamination 

 of the test substances. 



The microscope used was a long arm Zeiss binocular with as 

 objectives and number 4 eyepieces. The camera lucida draw- 

 ings were made in the ordinary way. 



METHODS 



The method of work was very simple. A small quantity of 

 the powdered substance which it was desired to use, was poured 

 out from the container on a clean glass slide lying on the stage. 

 The microscope arm was then swimg over it. A particle of the 

 desired size was then selected and transferred with the glass 

 needle to the slide or petri dish containing the ameba whose be- 

 havior was to be tested. Frequently some difficulty was encoun- 

 tered in pushing particles through the surface film. But once 

 through the film, the particles were placed wherever they were 



