REACTIONS OF AMEBA TO PROTEINS 55 



more than probable that a large number of tests with a considera- 

 ble number of substances will be necessary to detect and eliminate 

 errors arising from incomplete knowledge of the physiological 

 action of the test substances due to the presence of chemically 

 imperceptible impurities. 



Moreover the insolubility of some of the substances such as 

 globulin, lactalbumin, ovalbumin, etc., is influenced to some 

 extent by substances, organic and inorganic, held in solution in 

 the water in w^hich the amebas live. Since it is experimentally 

 impossible to keep pure the water in which the amebas may be 

 placed for observation, on account of their excretoiy products 

 diffusing out, the proteins themselves may possibly become 

 slightly soluble when these excretory substances come into con- 

 tact with them. On the other hand it should be pointed out 

 that the age of some protein compounds, especially albumins, 

 affects their solubility — the older they become, the more 

 insoluble. 



In view of all these disturbing factors attending the use of 

 proteins as test substances, it is evident that the observed re- 

 actions must be interpreted with care. 



EXPERIMENTS WITH GLOBULIN 



Merck's globulin with subtitle 'crystallin' was used. When- 

 ever the word globulin is used unqualified in this paper this 

 product is meant. A few trials were also made wdth a purer 

 ovoglobulin on raptorial amebas (the only kind of amebas ob- 

 tainable at the time) but no definite results were procured. 

 The solubility of Merck's globulin was tested by soaking for 

 some hours a few small particles in a drop of distilled water 

 on a clean glass slide and then evaporating the water. By ex- 

 amination with the microscope no difference could be observed 

 between the slight amount of residue of such a drop of water 

 and one in w^hich no globulin had been soaked. Similar experi- 

 ments were also made with tap water with similar results. If 

 any of the globulin went into solution therefore, the amount was 

 excessively small. 



' See Postscript on p. 79. 



