RELATIONS OF BURSARIA TO FOOD ' 3 



MATERIAL AND METHODS 

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Simple types of the three classes of food were found in lipoid- 

 free egg yolk (vitellin), pure olein, and starch grains of various 

 kinds. Potato starch was the most serviceable because grains of 

 a very uniform size can be obtained by repeated decantation of 

 a suspension, and hence results may be expressed quantitatively 

 in terms of unit volume. Fresh hard boiled yolk — a combina- 

 tion, chiefly, of lipoids and protein — was also used. Olive oil 

 of the best grade obtainable gave the same results as prepared 

 olein. * 



From the yolk of the hen's egg was prepared a protein (viteHin) 

 that was perfectly lipoid-free, so far as could be determined; 

 this was done as follows: An egg was boiled to hardness (15-20 

 minutes), and the granular portion of the yolk was kneaded 

 gently to a moist, fine, floury pulp. This was placed loosely in a 

 Soxhlet apparatus and extracted with an alcohol-ether mixture, 

 for eight to ten hours; in this way the fat and lecithin were re- 

 moved. The vitellin was then washed several times with fresh 

 alcohol-ether mixture, removed from the Soxhlet and while still 

 moist, gently kneaded to a fine white powder. This was left to 

 dry at 25°C. for twenty-four hours. After drying was completed 

 the residue was gently rubbed between sheets of filter-paper. 

 When the steps mentioned above were carefully carried out, the 

 grains of vitellin were found to be separated. This white dry 

 powder was kept in a dry bottle in a cool place, and used as a 

 food stock. 



When the animals were to be fed, a suspension of the powder 

 was made in tap or distilled water and rubbed up; then left to 

 settle, and the supernatant liquid with the smaller particles was 

 poured off. This process of separating the smaller grains from 

 the larger ones was repeated until a perfectly clear suspension 

 of the protein replicas of the uniform hard-boiled grains was 

 obtained. 



It is important to note that some eggs yield much more uni- 

 form yolk grains after boiling, than others. Only those eggs 

 were used in this work which were satisfactory in this respect. 



