45 



operations to see if it was possible to concentrate its action 

 by either evaporation to dryness and resolving it in small 

 quantities of liquids or by making tractions of the pro- 

 teins in the tissue extract according to the generally known 

 chemical principles . Most of these experiments gave, how- 

 ever, negative results, but Iney are anyway rather valuable 

 because they contribute to characterize these substances 

 and furnish a base for further experimentations. 



The material I used for all the experiments, was tissue 

 juice prepared from fresh chicken embryos. The tissue 

 juice was prepared in the usual way as it designedly is done 

 for the culture medium. Seven to ten days old chicken em- 

 bryos were hashed up to a fine pulp with a pair of scissors; 

 the pulp is cenlrifuged and the supernatant, clear, s,lightly 

 mucous fluid is drawn off with a pipette. The fluid may 

 simply be termed the •extract". At other times the extract 

 was prepared in a slightly different way. To the embryo?: 

 were added kieselgur and Ringer solution and they were 

 ground in a mortar. It was found, that the extract ob- 

 tained by the latter method possessed a much less activating 

 power than did the extract obtained by cutting the embryos 

 into small pieces with scissors. This fact agrees very well 

 with the observation made on fresh embryonic extract, 

 that it loses greatly its activity by merely shaking for some 

 length of time. Carrel and E b e 1 i n g ^^) observed also 

 that serum being shaken for some time lost a good deal 

 of its activity. It is probable therefore that the grinding with 

 sand or kieselgur effects the substances in a similar way as 

 does the shaking. This shows, however, that the growth pro- 

 moting substances must be of an extremely unstable nature. 

 The first method was therefore selected for the prepara- 

 tion of the embryonic tissue juice. The old strain of fibro- 

 blasts 16*) (ten years old) was used as a reagent in the 

 chemical experiments. Special techniques were developed 

 for working aseptically during the different chemical and 

 physical manipulations. 



