244 SOME ASPECTS OF ECOLOGY 



soluble vitamin B, which is necessary for the higher animals. 

 Baumberger, two years later, advanced evidence which led him 

 to conclude that the substance necessary is yeast nucleoprotein. 

 Bacot and Harden (1922) grew Drosophila larvae aseptically, and 

 were able to confirm that this insect requires vitamin B for its 

 complete development, but not vitamin C ; at the same time, it 

 was able to develop in the presence of very small quantities of 

 vitamin A, and it was uncertain whether the latter was essential 

 or not. 



Certain other insects have also been the subject of vitamin 

 investigation. The experiments of Wollman, for example, with 

 the blow-fly Calliphora and the cockroach Blatella appear to lead 

 to the conclusion that vitamins are not essential for the growth 

 of either insect. Notwithstanding sterilisation precautions, the 

 complete elimination of micro-organisms from within the eggs or 

 larvae cannot be ensured, and these alone may contain sufficient 

 vitamin to enable the insect to undergo development in sterilised 

 food. The careful experiments of Richardson (1926), with 

 reference to the Mediterranean flour moth (Ephestia kuhniella), 

 afford evidence that vitamins are necessary for the complete 

 development of that insect. Full growth occurs when the insect is 

 reared upon normal entire-wheat flour, but when the latter be 

 treated to prolonged extraction with chloroform, all the larvae, 

 when fed on the residue, die at an early age. If, however, the 

 extract containing the growth-promoting substance was added to 

 the wheat, residue growth of the insect took place at nearly normal 

 rate. Similarly, ether-extracted wheat allowed of but few larvae 

 to reach the pupal stage, but when the extract is added to the flour 

 residue practically normal growth results. It would appear that 

 the extract in these experiments contains a substance similar to, 

 or identical with, vitamin A. When an ether extract of egg- 

 yolk containing vitamin A was added to the wheat residues of the 

 previous experiments, the larvae grew normally. Richardson also 

 found that highly milled patent flour retarded larval growth and 

 resulted in moths of significantly lower weight. Since, however, 

 the growth value of this medium is considerably improved by the 

 addition of an alcoholic extract of yeast, it is believed that its 



