January 29, 1915] 



SCIENCE 



169 



and to some important omissions in bibliog- 

 raphies may well be corrected in a later edition. 

 Charles Atwood Kofoid 

 Uniyersity op California 



SPECIAL ABTICLES 



THE SIMPLEST CONSTITUENTS REQUIRED FOR 



GROWTH AND THE COMPLETION OP THE 



LITE CYCLE IN AN INSECT (dEOSOPHILA) 



The green plants are able to build up all tbe 

 complicated proteins, polysaccharides and fats 

 of their tissues from nitrates, phosphates and 

 sulphates, on the one hand, and from C0„, on 

 the other. Those microorganisms which can 

 not form sugar or starch from CO. must be 

 offered a more complicated compound than COj 

 for the synthesis of their carbohydrates. They 

 may be able, however, to form all their pro- 

 teins from an ammonium salt or a single 

 amino-aeid. This astonishing synthetic power 

 is in sharp contrast to the behavior of mam- 

 mals which, according to Osborne and Mendel, 

 can not grow unless one or more proteins are 

 offered to them, for the reason that they lack 

 the power of manufacturing the majority of 

 amino-acids required for the building up of 

 the proteins of their body. 



Eecent experimenters have pointed out that 

 in addition to the chemically well-defined con- 

 stituents of food, other more or less mysterious 

 constituents, which only the living body can 

 produce, are required for the growth of mam- 

 mals. Thus Hopkins, and Osborne and Mendel 

 have found that certain unknown constituents 

 of milk or butter have a specific effect upon 

 the growth of rats, and Allen has found that 

 even a Diatom (Thalassiosira) grows incom- 

 parably better if one to four per cent, natural 

 sea water is added to the culture medium. 



It seemed of interest to find out which sub- 

 stances are required for the growth and the 

 completion of the life cycle of such highly 

 specialized animals as insects. The banana 

 fly (Drosophila) , on account of the ease with 

 which it can be raised, served as an object for 

 our investigations. 



We wish to report only on one group of the 

 experiments we have made, namely, those re- 

 ferring to the source of nitrogenous compounds 



required for the growth and the complete life 

 cycle of these insects. Our culture medium 

 consisted of a solution of the purest cane sugar 

 or grape sugar obtainable, or of both, to which 

 certain inorganic salts (Kahlbaum's purest) 

 were added. To this medium was added a very 

 small quantity (about 0.25 gram) of mechan- 

 ically macerated Schleicher and Schiill filter 

 paper (No. 589, "Blue Eibbon"), chiefly to 

 keep the flies from drowning and to facilitate 

 the raising of the larvse. Dr. Levene was kind 

 enough to have a nitrogen determination of 

 the filter paper made, which showed that its 

 nitrogen content is 0.008 per cent. In such a 

 solution the flies laid their eggs. The larvse 

 hatched and increased slightly in size during 

 the first days, but then their growth stopped, 

 although they lived for a considerable time. 

 If, however, a small quantity of one or two 

 amino-acids, e. g., alanine or glutaminie acid 

 or others, or certain ammonium salts, e. g., 

 ammonium tartrate or succinate or a combina- 

 tion of one ammonium salt and one amino- 

 acid, was added, the larvK grew to fuU size 

 and metamorphosed into pupse and normal 

 flies. 



In these experiments everything used was 

 sterilized, and in addition the culture media 

 were heated for fifty minutes to about 100° 0. ; 

 but since the flies were not sterile, the develop- 

 ment of bacteria was ncjt excluded. The flies 

 were removed as soon as a sufficient number 

 of eggs had been laid. In the majority of 

 experiments no visible fungus formation 

 occurred. When visible fungus growth took 

 place the larvae, as a rule, soon died or failed 

 to develop. 



If in these experiments the larvae were 

 actually able to manufacture all the compli- 

 cated nitrogenous compounds of their body 

 from one or two amino-acids or from one 

 ammonium salt, without the aid of bacteria, 

 it would indicate a power of synthesis equal 

 to that of bacteria. In this connection it is 

 of importance that the larvae of the banana fly 

 can be raised on their natural vegetable food 

 without bacteria. Thus Guyenot has succeeded 

 in raising aseptically forty successive genera- 

 tions of Drosophila, thereby proving that for 



