14B 



sc'vci'iil (hiys. Ilu- lilc of licarl (issue \\;is miicli loii.m'r lli;iii 

 Ihiil of llic strain ol' lihrohiasls. This plu-iioiiu'iioii is cx- 

 plaini'cl l)y llic IVcsli ciiihi-voiiic lu-arl coiilainin^f llicsc ac- 

 ccloralinj.', siibslaiiccs as tlu-y ai'c loimd in llic ('inl)i'vonic 

 juice \vlu'i-t-as llie old strain ol' fibroblasts contains ver\ 



little c()nii)are(l with the fresh tissue. 



In order to learn wiielher the end)i"yonic (issue juiei'. 

 which causes the indefinile niulliplicalioii of fibroblasts 

 in vitro, renders possible llu' utilization by Ihe cells of 

 substances contained in tlie serum or the fibrin oi- wiietbei' 

 it su])i)lies itself tlie material required by the cells for 

 their proliferation, (barrel and I" b e 1 i n g ■'•*; made the 

 following exi)erimenls. 



In some experiments tlie media were composed of a 

 constant amount of fibrinogen suspension and end)i\vonic 

 tissue juice and varied tpianlilies of serum and Tyrode 

 solution. The results of these experiments showed that the 

 lack of serum, or its pi'esence in low or high concentra- 

 tions, had no influence on the I'ate of growth. 'J'his demon- 

 strated that in the jiresence of embryonic tissue juice, there 

 was no utilization of the serum or fibrin to a measureable 

 extent. 



In other experiments the embryonic tissue juice was 

 added in increasing amounts to a constant amount of serum 

 and fibrinogen. The results of these experiments were that 

 increases in concentration from to 10 jx'r cent of embrj^- 

 onic juice brought about a greater change in activity of 

 the cells than inci'cases from 10 — 80 "o. After the concen- 

 tration of the juice in Ihe medium had reached 10 per 

 cent, no further increase was observed at any higher con- 

 centration, (Fig. 30). 



Already in the early ])eriod of tissue cultivation C a r- 

 reP'^) discovered that by cultivating connective tissue in 

 the plasm: of chickens of different ages, he found that the 

 growth was more abundant in the plasma of the younger 

 than in that of the older animals. This fact suggested Ihat 



