41 



another chapter. It may be mentioned here, however, in 

 connection with the discussion of the relation of sohd 

 frameworlv to the cell growtli and the cell shaj)e, that 

 as soon as the cotton Ihreads are as])irated, the remain- 

 ing cells in part of the drop of tissue juice on the cover- 

 slip immediatelj' become spherical. The remaining cells con- 

 tracted and agglutinated to an aggregation of round cells 

 9 and looked like leucocytes. Also, the cells asi)irated in the 

 pipette and distributed in the plasma which latei' coagu- 

 lated were all spherical, but nevertheless alive, with a 

 lively ameboid movement and they appeared later in the 

 clot as typically spindel-shaped fibroblasts. 



THK (;r()\\'th promoting substances. 



II has been known for a long time (Carrel, 1913)'^'^) 

 that the culture medium consisting of coagulated plasma 

 only, was not sufficient to keep the tissue cells alive in 

 vitro during long periods and just recently Carrel and 

 E b e 1 i n g f 1921) •*-) ^^) have shown that even the homolo- 

 gous serum has an inhibiting influence on the rate of growth 

 of fibroblasts. In other words, the indefinite multiplication 

 of fibroblasts is due neither to the fibrin nor the serum, but 

 lo substances contained in the embryonic tissue juice. 



In media composed of a constant amount of fibrin and 

 a mixture of Tyrodes solution and serum in varied concen- 

 trations. th(^ amount of growth appeared to be independent 

 of the concentration, and even of the presence of serum, 

 According to Carrel and E b e I i n g ^^^ ) neither serum 

 nor fibrin is utilized by the cells. Carrel ^^) found, that 

 Ihe rate of growth of fibroblasts grown in fibrin fixed in, 

 formaldehyde solution did not differ from that in normal 

 fibrin, AA hen fragments of the old strain of fibroblasts 

 were cultivated in media containing a constant amount of 

 serum and fibrin, and the concentration of embryo juice 

 was varied, the rate of growth was found lo be a function 

 of the concentration of the embryonic juice in the medium. 





