36 



J. PERCY BAUMBERGER 



TABLE 11 



FOOD MATERIAL 



Fruits 



Vegetables. 



Yeast 



B. prodigiosus. . . 

 Putrefactive bac- 

 teria 



Mushroom 



AUTHORITY 



Atwater ('17) 

 Atwater ('17) 

 Stutzer ('82) 

 Atwater ('02) 

 Kappes ('89) 

 Nencki and 

 Scheffer ('80) 

 Atwater ('17) 



1 Probably largely starch in the compressed yeast. Glycogen makes up 31 

 per cent (by dry weight) and gumes 6 per cent of the yeast. 



viz., glycocoU, alanine, valine, leucine, proline, phenylalanine, as- 

 partic and glutamic acids, tyrosine, tryptophane, and probably 

 serine and cystine (Meisenheimer, '15), and it is therefore not 

 surprising that it forms, with sugars and salts, a complete food 

 for Drosophila. As the preceding experiments show that Dro- 

 sophila larvae require more concentrated protein than is present 

 in the substratum, it is apparent that the habits of the insect are 

 for this reason, adapted to the use of the richly protein micro- 

 organisms as food. 



d. Function of yeast in the ecology of Drosophila. The func- 

 tion of yeast in a Drosophila culture is clearly defined by the fol- 

 lowing two experiments: 



1. Larvae grow slowly on a weak, cold-water extract of asep- 

 tic unfermented bananas and remain at about the same size for 

 a period five times the normal life and then die without pupating. 

 If this culture is left open for a few minutes, in such a position as 

 to allow a few fungous spores to fall into the medium, the larvae 

 will increase their rate of growth and pupate in a few days. 



2. Larvae on sterile 1 per cent yeast agar grow to a length of 

 4 mm. in twenty days and die without pupating. If the culture 

 is inoculated with a minute quantity of yeast cells the larval 

 period is only seven days and is followed by pupation. In both 

 cases the yeast cells remove, by adsorption from the medium, 

 the amino-acid molecules in their immediate neighborhood. As 

 this goes on a steady diffusion of amino-acid molecules occurs 



