84 THE VITAMINES 



yeast substance was heat-resistant but lost some of its activity on 

 treatment with cold or hot alcohol. Drosophila is a monophageous 

 animal and yeast seems to be the only adequate food for it. These 

 flies can live in any nutritive solution that is suitable for the growth 

 of yeast, and the medium is usually infected with this organism. 

 Loeb and Northrop rightly observed that in considering the synthetic 

 abilities of the higher animals, one must not lose sight of a possible 

 cooperation of the intestinal bacteria. Loeb and Northrop (234) and 

 also Northrop (235) showed by means of a specially planned series 

 of experiments that the developmental stages of flies (except imago) 

 can be prolonged from 8 to 17 days at will. They believed that the 

 three stages of metamorphosis could be regulated by the formation 

 and disappearance of three different substances. 



In a later work, Northrop (236) investigated the role of yeast in 

 the nutrition of flies. He found that the number of flies that could 

 be developed on a certain quantity of yeast could be increased by 

 the addition of bananas, casein or sugar. The rate of growth on a 

 combination of yeast and bananas is greater than on yeast alone. 

 In mixtures containing a small amount of yeast, growth proceeds 

 more slowly, and in a dilution of 1 to 128, it becomes entirely abnormal. 

 Kidney, liver, dog pancreas, mouse liver, and bodies of flies them- 

 selves were suitable for the growth of the larvae, while sterilized 

 spleen, heart muscle, suprarenal glands, thyroid and blood of the 

 dog were unsuitable; the addition of muscle tissue, testicles and 

 sterilized thymus gland of the dog, rabbit and calf, resulted in the 

 development of some chrysalis, but growth proceeded slowly and 

 the flies appeared dwarfed. Robertson's tethelin (lipoid from the 

 hypophysis) was inactive. 



Guye'not (237) attributed to the vitamines some part in the devel- 

 opment of fly larvae of the Drosophila ampelophila. Baumberger 

 (238) investigated some species of flies and came to the conclusion 

 that Drosphila melanogaster can live on fermenting fruits and also on 

 yeast protein. A combination of yeast, nucleo-proteids, sugar and 

 a salt mixture provides a suitable food for larvae. Other kinds of 

 flies, like Musca domestica, Desmotopa, Sciaria and Tyroglypha, can 

 all thrive on microorganisms. 



From this chapter, we see, especially from the work of Loeb, that 

 flies need vitamines for their development, and that vitamine B 

 plays the most important part. 



