II 



contrary liad n toxic cited on llic tissue cells. In tne ex- 

 piMiineiils care was naturally taken to keep the culture 

 medium isotonic. 



The influence of extracts from various tissues, from em- 

 bryonic as well as adult tissues, has been tried in the cul- 

 tures (C a r r e 1 ^•^). W a 1 1 o n ^^''). As known. ("- a r r e 1 found 

 that extracts of ail (lifrcrenl kinds of tissues actixalcd llic 

 growth of fil)r()l)lasls. The di'gri'e of acceleration \aried 

 much. Mmhryonic tissue extract was the most active, and 

 extracts of adult s|)leen and Hie \\ o u s sarcoma were almi)s> 

 as active as Hie extract of chicken emi)ryos. The effect of 

 extracts of the thyroid gland and muscle of the dog on the 

 growth of periosteum was very marked, hul thyroid exii'act 

 was more active than muscle extract. Carrel already ob- 

 served before he worked with tissue cultures, that i)ulp of 

 embryonic tissues placed in an open wound I'esuited in a 

 rapid cicatrication. Also \\alton '"") tried the effect of 

 extracts of various tissues on the growth of mammalian, 

 tissue in vitro. He found thai most extracts stimulate the 

 growth and that an extract of the liver has an inhibiting: 

 effect. Very recently (barrel •'^) has shown that an ex- 

 tract of leucocytes has a marked activating effect on the 

 growth of fibroblasts and that leucocytes in culture are 

 secreting substances which activate the gi-owth of fibro- 

 blasts. fTrephones). '^^). 



PHYSICO-CHEMICAL STUDY OF THE NATURE OF THE 

 GROWTH-PROMOTINCx SUBSTANCES. 



To understand the mechanism of growth, it would be 

 necessary to investigate the nature of the growth-promo- 

 ting substances. If we, for instance, were able to isolate 

 the factor which increases the velocity of cell multiplication, 

 many hitherto unknown phenomena could be understood 

 and processes of repair could i)robal)ly be accelerated. 



I began therefore to treat the embryonic tissue juico 

 in different wavs, to break it down bv various chemical 



