226 A. A. SCHAEFFER 



the formation of the food cup the coleps stopped moving, and at 

 the same time the water disappeared from the food vacuole. 

 The coleps became separated from the globulin, and about 

 twelve minutes after the food cup was formed the globulin was 

 excreted. 



The results of these experiments leave no doubt of the fine 

 sense of discrimination which ameba is capable of exercising. 

 Not only does ameba discriminate before coming into contact 

 with objects, but also after they are in the food cup and even 

 after they are imbedded in the protoplasm. The experiment 

 recording the ingestion in the same food cup of globulin and a 

 coleps indicates this, for after these substances were imbedded 

 in the protoplasm a coleps was preferred to globulin. 



The experiments with egg albumin and globulin, and egg 

 albumin and silicic acid, show clearly that the presence of a 

 substance in solution only is not' sufficient to attract ameba, 

 nor to cause ingestion, but that the substance must be actively 

 diffusing from a definitely localized region. 1 



THE EFFECT OF MECHANICAL STIMULATION 



It became evident as the feeding experiments went on that 

 movement of food objects is an important factor in ingestion, 

 and sometimes indeed a determinining factor. A number of 

 experiments were then projected to see especially what the 

 effect of water vibrations is upon ameba, and whether vibrations 

 of themselves are capable of causing a definite change in behavior. 



It is to be regretted that but few drawings can be presented 

 in illustration of the gradual change in behavior that is pro- 

 duced by mechanical stimulation; but it was impossible to make 

 a series of drawings for each experiment, as was done in the 

 other cases, for the drawing hand of the experimenter was em- 

 ployed in vibrating the needle. Consequently with the excep- 

 tion of one experiment — 194-197 — which is represented by 

 memory drawings made immediately after the experiment, only 

 the final stages are illustrated by camera lucida figures. The 

 different kinds of objects used in these experiments are fairly 

 representative. Several kinds of insoluble indigestible sub- 

 stances, as well as food substances, were employed. 



3 There is some evidence here that two particles of different degrees of attrac- 

 tiveness when encountered separately, are reacted to, when lying close together, 

 as one (the more attractive) being attractive and the other (the less attractive) 

 repulsive. 



