THE MITOTIC CYCLE 



unorganized growth, of osteogenetic cells into true bone was achieved in 

 vitro by the 'ascending range' method of cultivation in extracts from 

 successively older embryos with each renewal of the culture medium 

 (Gaillard109). 



Adult tissue extracts 



Conclusions about the effects of adult tissue extracts vary widely. This 

 may be due to differences in technique and in methods of measuring 

 'growth'. Carrel^^ reported adult spleen extracts to be more active 

 than kidney, muscle or thyroid and found extracts of the Rous chicken 

 sarcoma effective. Heaton^io found adult spleen the least effective of a 

 series of tissues of which bone marrow was the best, followed by 

 brain, kidney, heart, voluntary muscle, pancreas, intestine, thymus, 

 lung, ovary and testis. In agreement with Walton,^" he found that the 



'^ff ^^' 



Figure 6i 3-dimensional representation of the effect on the growth of heart 

 fibroblasts from a 7-day chick embryo of different concentrations of press 

 juice from 4-, 7-, 10-, 15- and 18-day chick embryos, and also from 

 hatched chick (C.S.) and from adult (H.S.). From Gaillard"^ {By courtesy, 

 Hermann et Cie) . 



growth of fibroblasts was inhibited by liver extracts. The order of 

 activity of adult and growing fowl tissue extracts given by Trowell 

 and WillmerIi^ descends from brain to thyroid, thymus, testis, ovary, 

 bone marrow, liver, kidney and muscle. Brain was found by Hoff- 

 MANN^^^ to be the only effective extract from a series of rat tissues 

 tested on chick tissue cultures: heart extracts had no effect and liver, 

 kidney, lung and spleen were inhibitory. The only claims for greater 

 activity in an adult tissue than in embryo extracts are those of Dol- 

 jANSKi and HoFFMANN^i* and Hoffmann et alii^^^ ^^^ who obtained 

 more rapid growth of chick fibroblast cultures with adult chicken 

 heart extract than with the usual chick embryo extract; optimal 

 concentrations of the two extracts stimulated mitosis to the same degree 

 (Margoliash and Doljanski^^'^). Area increases of the same order as 

 produced by chick embryo extracts were achieved with adult sheep, 

 cow, rabbit and dog heart extracts (Doljanski et alii^^^). Sustained 

 growth of adult fowl heart tissue has been achieved in a medium of 

 entirely adult origin (Doljanski and Hoffmann^^^). 



174 



