42 J. PERCY BAUMBERGER 



found that certain crystalline solids left on the filter after filtering 

 autolyzed yeast could be substituted for lecithin. These crys- 

 talline substances are probably also constituents of yeast nucleo- 

 protein. 



Loeb and Northrop ('17) have recently used glucose beef agar 

 for maintenance of larvae and adults so that the temperature 

 coefficient of the duration of life could be determined, and 

 Northrop ('17 a) has shown that the total duration of the life 

 of Drosophila can be increased by retarding the growth of the 

 larvae, as the pupal and imaginal periods do not seem to change 

 with the increased larval life. These results are entirely com- 

 parable to those given on page 30. Northrop ('17 b) describes 

 expermients which have led him io the conclusion that yeast sup- 

 plies a special substance necessary for the growth of Drosophila 

 larvae. This author finds that banana, casein, and sugar sup- 

 plement yeast as a food for larvae and permit the development of 

 a larger number of adults than could take place on yeast alone. 

 The optimum mixture contained 33 per cent yeast, and as the 

 amount of yeast decreased the number of adults reared became 

 less and growth of larvae slower until at a proportion of yeast of 

 1 : 128 the growth of larvae became abnormal. Kidney, liver, 

 and pancreas of dog were adequate foods for larvae, but spleen, 

 heart muscle, muscle, blood, adrenal, and thyroid were not a 

 complete diet for the insect. The author concludes that the 

 special substance required for growth cannot be obtained from 

 protein or carbohydrates. From my experiments I have evidence 

 (p. 14) that banana and sugar have food value for Drosophila 

 larvae, and to this extent my results are in accord with North- 

 rop's, however, since the insects can develop normally on yeast 

 nucleoprotein, sugars, and salts it seems probable that the special 

 substances required for the growth of Drosophila are included in 

 nucleoprotein. 



In summing up the results of my experiment I conclude: 1. 

 Drosophila normally feeds on fermenting fruit, obtaining a large 

 part of its nourishment from the microorganisms, especially 

 yeasts, which are in a loose symbiosis with the insect. 



2.. Dead or living yeast is a complete food for Drosophila. 



