145 



never observed, it is a mere survival ol" tissues. Tlie 

 addilion of enil)ryonic tissue juice to the plasma activates 

 the cell-division and bi'in^js about an immense increase 

 in mass of llie tissue. The strain of fibroblasts of Carrel 

 derived from a small fragment of embryonic heart has pro- 

 duced about 30,000 cultures in 9 years and is as active to- 

 day as at the beginning of its life. Carrel and Ebeling^^) 

 found that connective tissue grew as extensively in fibrin, 

 fixed by formaldehyde as in normal fibrin, therefore the 

 role of fibrin must be considered as purely mechanical. 



The influence of serum was investigated by (barrel and 

 El>eling f'-^; by measuring the rate of growth of fibro- 

 blasts in media containing no serum. The fibroblasts 

 were cultivated in media composed of fibrinogen sus- 

 pensions and of T y r o d c solution and containing no 

 serum or serum in varied dilutions. The fibrinogen 

 was prepared according to a technique described by E b e- 

 lingi*'- The results of the growth of fresh embryonic 

 heart tissue in media containing from to 90 per cent 

 serum showed that the cells in their process of multipli- 

 cation do not make use of the serum to an extent measure- 

 able by the present technique. The growth of embryonic 

 heart appeared to be independent of the concentration of 

 the serum as long as the amount of fibrin was not modified. 

 Also the old strain of fibroblasts was cultivated in media 

 containing serum from 2.37 to 80 per cent; there was not 

 observed any difference between the amount of growth of 

 the fragments; the rate of growth decreased rapidly and 

 death occurred usuall}' after the 6th or 71 h passage. 



When fresh embryonic heart tissue and connective tis- 

 sue from the old strain were cultivated in serum and fi- 

 brinogen only, there was a striking difference between 

 the growth of the two fragments. As soon as the strain of 

 fibroblasts was placed in plasma alone, the rate of multipli- 

 cation of its cells decreases, while under the same conditions 

 the activity of a fragment of embryonic heart increased for 



10 



