4 • E. J. LUND 



It seems highly probable from the results, that all traces of 

 lecithin and fat had been removed by this method. Cold ether 

 or cold alcohol extraction alone is not sufficient to remove all the 

 lipoid content from hard boiled yolk. This will appear from 

 results (p. 29) of experiments in which such vitellin grains were 

 used. 



By this method of preparation, lipoid-free vitellin may be ob- 

 tained in very uniform grains, and this permits one to fulfill a 

 condition most important for precise experimentation. One 

 can feed definite unit quantities to a single cell; and this makes 

 it possible to attack a number of questions regarding metabohsm 

 that would otherwise be inaccessible, and to express the results 

 in quantitative terms. 



Fresh hard-boiled yolk served as a protein-lipoid diet, which 

 could be fed in the same way, for the vitelHn grains are simply 

 the protein matrix of the fresh hard boiled yolk grains in which 

 the lipoids and any other alcohol-ether soluble substances are 

 imbedded. 



There is, of course, no means of knowing whether the vitellin 

 of the unextracted yolk grain does not undergo change during 

 ether-alcohol extraction; but the fact (demonstrated by the 

 experiments) that in the food vacuole digestion of the protein 

 in these two forms occurs in the same way and with about equal 

 readiness, shows that the process of fat extraction does not alter 

 the chemical or physical nature in such a way as to interfere with 

 the digestion and resorption of the vitellin. 



In all the experiments where necessary, the animals were 

 placed in 500 cc. of tap water twenty-four hours previous to 

 feeding. The result of this was that the food and debris con- 

 tained in the cell had been discharged during the twenty-four 

 hours of starvation, and hence a cell with perfectly clear cyto- 

 plasm was obtained for the experiments. By this means a parti- 

 cularly desirable uniformity in physiological condition of the 

 organisms was obtained. The material was from the same wild 

 stock cultures as that used in the experiments reported in my 

 earlier paper. 



