THE VITAMINES IN THE ANIMAL KINGDOM 83 



could be filtered through a Berkefeld filter, but not through a Cham- 

 berland filter. Regarding the foregoing, it appears likely that a new 

 field for vitamine research is opened up. 



INSECTS 



We have to deal here with the very interesting studies of Jacques 

 Loeb (231). He demonstrated that a type of fly (Drosophila) could 

 attain the larva stage upon a solution of cane sugar and salts, together 

 with the addition of filter paper. The larvae grew quickly, especially 

 on the addition of alanine or an ammonium salt. In this particular 

 instance, no attention was paid to the influence of the bacteria on the 

 substrate. Five successive generations of the banana fly (232) were 

 grown on a solution of glucose, cane sugar, ammonium tartrate, citric 

 acid, di-potassium phosphate and magnesium sulphate. As Loeb 

 himself observed, it was not quite certain that the solution was free 

 of bacteria; the presence of yeast in particular was not excluded. 

 In these experiments, the flies themselves were not sterile and there- 

 fore Loeb and Northrop (233) started experiments with flies hatched 

 from eggs sterilized by a sublimate solution. Twelve sterile genera- 

 tions were cultivated in this manner, carefully protected from every 

 possibility of contamination with yeast growth. The nutritive solu- 

 tion used was composed of 450 grams baker's yeast and 50 grams 

 citric acid (used for the purpose of decreasing the danger of infection 

 during the various manipulations) in a liter of water. In a great 

 number of experiments, the investigators showed that on another 

 medium, for instance, filter paper and cane sugar, with the addition 

 of salts, and likewise with the addition of casein, edestin, egg albumin, 

 milk, or a mixture of amino acids, the larvae attained normal size 

 but could not be brought to the stage of metamorphosis. Sterile 

 flies, grown on sterile bananas or potatoes, showed no sexual develop- 

 ment. The results with yeast as substrate were different; here, all 

 the substances are manifestly at hand, which are indispensable for 

 the growth and development of flies. Butter, nucleic acids, thymus 

 and thyroid extracts were without influence, and the authors believed 

 that these substances are different from those which are of importance 

 for pigeons, rats and other warm-blooded animals. This view must 

 naturally undergo a slight modification, since there is obviously no 

 reason to differentiate between flies and warm-blooded species. The 



