78 ■ A. A. SCHAEFFER 



raptorial ameba. If it had been a granular ameba such behavior 

 would have been significant, for it would not have been expected. 

 Keratin can be sensed at a considerable distance, apparently 

 about 100 microns or more. 



EXPERIMENTS WITH FIBRIN 



The fibrin used was of a commercial variety and probably not 

 carefully purified. It is however a very insoluble substance, and 

 for exploratory work its use may be permissible. 



In the path of a raptorial ameba that had eaten a grain of 

 globulin was placed a grain of fibrin (1004). The ameba moved 

 toward the fibrin but before it came into contact with it a pseur 

 dopod was thrown out on the left through which the ameba moved 

 away. The same grain of fibrin was eaten (imperfectly?) when 

 agitated, but was excreted four minutes thereafter. 



In another experiment, not illustrated in this paper, a grain of 

 fibrin was eaten by a raptorial ameba in normal manner. Three 

 minutes thereafter a flagellate was eaten. Eight minutes after 

 this another flagellate was ingested at the posterior end where 

 the fibrin lay. But in spite of these hindrances to the excretion 

 of the fibrin, it was egested sixteen minutes after it was eaten. 



Fibrin ranks with ovalbumin and keratin in the qualities that 

 stimulate the feeding reactions, 



SUMMARY 



1. Ameba eats isolated proteins. Globulin (crystallin) is eaten 

 quite readily and particles of it undergo reduction in size in the 

 body. Lactalbumin is sometimes eaten, but it is not nearly as 

 attractive a food as globulin. Ovalbumin is even less attrac- 

 tive than lactalbumin and is eaten only occasionally. Zein, 

 which can be more readily freed from impurities than the other 

 proteins mentioned, attracts amebas to move toward particles of 

 it but in no case does ingestion follow. It is possible therefore 

 that the attractive qualities of ovalbumin and lactalbumin are 

 due to minute traces of soluble impurities, although these pro- 

 teins were made as pure as the science of chemistry can now 

 make them. 



