ON THE FEEDING HABITS OF AMEBA 555 



interrupted. As far then as the raptorial amebas are concerned, 

 movement is by far the most important quaUty in food organisms. 

 With tliose of the granular type, movement of food objects is not 

 so important, but even here it is probably more important than 

 any other single quality. 



Reactions to very slightly soluble substances 



This group of test substances includes carmine, well dried old 

 egg white, india ink, and uric acid. The behavior of ameba 

 toward these substances is taken up first for the reason that 

 camiine, the chief representative of this group has been used 

 more widely in experiments upon one-celled animals than any 

 other substance. Carmine is indeed the classic substance for 

 this purpose, having been used by Count v. Gleichen Russwurm 

 in feeding protozoa as far back as 1777. 



Carmine. The camiine used in these experiments was Griib- 

 ler's Carmin rubr. II. In some cases it was used pure; in other 

 cases it was mixed with a slight amount of egg white (as it comes 

 from the hen's egg) and dried, to prevent the particles from fall- 

 ing apart when moved around in the water. The mixtures of 

 carmine and egg white were of several grades. Grade 2 was made 

 by adding just enough egg white to the carmine to form a very 

 thick paste. Grade 4 was made by mixing one part of carmine 

 with five of egg white. These mixtures were thoroughly dried 

 with heat but without coagulating the egg white. 



As thus made up the carmine-egg white mixture is a complex 

 substance, and is somewhat objectionable as a test substance on 

 this account; for if a change in behavior is brought about by its 

 use, it is not certain just what part of the substance is respon- 

 sible for the change. But in this case it happens that the objec- 

 tion carries little weight, for in a number of instances pure car- 

 mine was employed and the reactions were very similar to those 

 where the mixture was employed. Pure cannine was used at 

 the beginning of the investigation of the feeding habits of the 

 ameba before the camera lucida was affixed to the microscope, 

 but an examination of the laboratory notes shows that pure car- 



