2l() 



of Ihc plasma modiuni f'l-oin solid to a licjiiid, all fiirllicr 

 oiilgrowlh Iroiii fhc IVagiiU'iil is iinijossibk'. When Iransfer- 

 rinj^ the lissuc IVom one culture lo another, it is possible- 

 only to carry o\'cr the orij^inal Iraf^uicnt which floats in a 

 lake of the licpiefied i)lasnia. After being brought lo a 

 fresh medium, the licpiefaction recommences, and so on 

 Continued this way. it is clear (hat we do not even gel 

 a multiplication of the tissue cells, but on the contrary 

 the tissue decreases in size and finally succumbs. 



Recently I therefore developed a new method for Ihc 

 cultivation of malignant tumor cells, which proved lo be 

 very satisfactory. The idea of the method I conceived by 

 considering the ability of the malignant tumor cells in. 

 vivo to invade the surrounding noruial tissues and displace 

 their cells. The question was, would the sarcoma cells, for 

 instance, also invade normal tissues added to the cultures 

 of sarcoma cells? 



The Rous chicken sarcoma was used in the experiments, 

 not because of the j)ecularities of this tumor 'infectious 

 fowl tumor,, but because it was a chicken tumoi\ which 

 would be rather easy to cultivate in its homogenic culture 

 media, and because the method of cultivating chicken tis- 

 sues in general is so j)erfect and well organised. 



The chicken sarcoma belonged to the type of polymor- 

 phous celled sarcoma. The grafts on chickens of all kinds 

 had a take of about 100 per cent. 



The sarcomatous tissue for cultivation was excised under 

 ether amesthesia from the lumor bearing animal, about 4 — 6 

 weeks after' inoculation. Sometiuies the tissue for the cul- 

 tures was taken from the original lumor and sometimes the 

 tissue was taken from metastasis in the lungs shortly after 

 the spontaneous death of the animal. 



The malignant tissue was cut into small j)ieces and 

 placed in the culture mediuui. usually couiposed of two 

 volumes of chicken plasma and a trace of freshly prei)ared 

 embryonic tissue juice. The gi-owth of the Rous chicken 



