37 



mixture of gelatine and agar, i. e.. agar which, for instance,, 

 contained gelatin evenly and mechanically distributed, then 

 probably the tissue cells could be (successfully) cultivated. 

 The ide-;! was, that at the temperature of the incubator, 

 '39 " C; the gelatin would become fluid in a meshwork of 

 agar and thus allow the cells to grow in between the lifpiid 

 gelatin and solid agar. These experiments were, however, 

 not at all successful. 



From these experimenls it would be concluded that it 

 is not true that growth of tissue cells can take place in 

 agar as such, only on the free surface under cover of a 

 liquid film. The explanation, therefore, why several investiga- 

 tors such as Leo L o e b, Lewis and Ingebrigtsen 

 have seen growth in agar is simply, that they have taken 

 the surface growth for an infiltration growth in the agar 

 itself Leo L o e b describes the penetration of epithelial 

 cells, for instance, in the agar; the agar has probably, in 

 the in vivo experiments, got some more oi* less minute 

 cracks into which the lymph has been soaked and therefore 

 created a medium for the ingrowth of the cells. I then 

 tried to crush the clotted agar, and by adding a liquid such 

 as embryonic tissue juice or serum to the fine agar par- 

 ticles, a growth could be obtained. This method did not seem 

 to have any advantages because of the much slighter trans- 

 parency of the medium for microscopical purposes and 

 the uneven growth. 



It was found in my ex])eriments that the quantitj' of 

 liquid added to the agar particles was most determining for 

 the outgrowth of cells. If there was an excess of liquid no 

 growth took place, but if there was added just enough to cause 

 the li((uid to stick by capillai'y suction to the surface of the 

 particles, an outgrowth of cells occurred. The same pheno- 

 menon was later observed by using other solids as a support- 

 ing apparatus (cotton, glass-wool). There seems to be an im- 

 portant connection with the surface forces and the migra- 

 tion of cells which also has been observed bv other investi- 



