TISSUE-CULTURE IN VITRO 



117 



the plasma in the ordinary technique, and it was therefore of 

 interest to use it. These curves express in percentage the 

 part played by age in the duration of life and in the activity 

 of proliferation. 



It can be seen that the drop is much more rapid in the 



/2o 



FIG. 24. DURATION OF LIFE 'iN VITRO' OF FIBROBLASTS AS A FUNCTION 

 OF THE AGE OF THE ANIMALS FROM WHICH THE PLASMA WAS TAKEN 



first years and especially in the first months. This indicates 

 that the inhibiting power of the plasma increases much more 

 rapidly at the beginning than at the end of life, and tends 

 towards a constant value. If these curves are now compared 

 with that of Fig. 26 representing the variations of the index 

 of cicatrization studied previously, it is obvious that a striking 

 similarity exists between them. This last curve represents the 

 evolution of i for a wound of 40 sq. cm. 



The growth index which can be deduced from CarreVs experi- 

 ments is therefore closely related to the index of cicatrization. 

 Both these indices are a measure of the irreversible trans- 

 formations progressively introduced into an organism by age. 



