153 



9'-») found that the tissue cells cannot obtain llu; nilrogen 

 necessar} tor their proliferation from chicken bouillon, egg 

 white, egg yolk or pure egg albumin. It was also obsen'ed'''; 

 that the addition lo a ])rotective medium of extracts of tis- 

 sues from adult animals, stimulated (he rate of growth ot 

 homologous fibroblasts. Also the addition of heterologous ex- 

 tracts or tissue juice stimulated a culture of fibroblasts to in- 

 crease in mass, at least for a time. It was shown that mouse 

 embryo juice was just as active on chicken fibroblasts as 

 the embryonic chicken juice. After 2() passages, the rate 

 of growtti of chicken fibroblasts was still practically the 

 same in both substances. Rabbit eml)ryo juice, and guinea pig 

 embryo juice showed almost as active on chicken fibroblasts 

 as the chicken embryo juice. 



Fibroblasts and epithelium ai*e not able lo multiply with 

 blood serum as the only nutrient. It is known thai tissues 

 of an adult animal, even an old animal, are able to grow 

 and multij^ly under the formation of a lai'ge amount of new 

 tissues, for instance when wounds are healing. Under the 

 process ot cicatrization of a wound in an animal of old age, 

 substances which stimulate the growth must be lil)erated. 

 Carrel"'^) found that leucocytes supply the adidt tissues 

 with substances which activate the rate of proliferation 

 in the same way as embryonic juice. The leucocytes remain 

 during the entire life of the organism, in the embryonic stage 

 of development and contain growth-promoting substances. 

 These substances could be extracted from leucocytes. (I a r- 

 rel'^^) also showed that living leucocytes during their life 

 in vitro, secrete growth-activating substances. He also found 

 that leucocytes are capable of setting free growlli-activating 

 substances in vivo. In making an ase])tic inflamnuition. small 

 sponges soaked with dilute hydrochloric acid, were placed 

 beneath the skin of chickens. The inflamed tissue was ex- 

 tracted with a small amount of Ringer solution and tested 

 against fibroblasts in cultures. The experiment showed that 

 the inflamed tissue, when quantities of leucocytes have ac- 



