117 



.if|-()\viiio; lil)i'()l)lasls could Ix' used ;i.s ;i i-(';in(.n( r,,|- (j^. 

 changt's occiin-iiii) in llic blood uiidci- llic inriiiciicc ol" 

 age. Loeb and \ o i- 1 li r o p ";«) came lo Ihc conclusion 

 ol" their ex])erinienls on llic Icnipcralnrc cocliicicnl ol" diir- 

 alion of life of Ihe frnililv Drosophila, liml llic duralion 

 of life was probably dclcnnincd l)y Ihc production of a sub- 

 slance leading lo old age. or by Ihe dcsli-uclion of a sub- 

 slaiicc normally preventing old age. In order lo know 



40 



e 



c 



•r-i 



ft— 

 o 



♦-> 



T3 



30 



20 



10 



^^.-^ """^ ' 



0^5 5 10 15 20 25 30 40 50 60 70 80 



Per cent of embpyonic tissue juice 



Fig. 30. 

 Relation between absolute increase of the tissue and tlie concentration of 



the embryonic juice in the medium. 



From Carrel and Ebeling: Multiplication of fibroblasts in vitro. Journ. 



of Exp. Med. 1921, XXXIV, 333. 



which of Ihese hypotheses was the righl one. Carrel and 

 E be ling 32) made a series of experiments on fibroblasts 

 enllivated in plasma from chicken representing different 

 ages. 



It was observed that Ihe growth of fibroblasts in plasma 

 from young chickens was more abundani than thai in 

 the plasma from the old chickens^-), ^^hen a fragment of 

 connective tissue from the old strain was placed in plasma 

 alone, a sudden drop in Ihe velocity of growth was ob- 



10* 



