458 BIOLOGY: GENERAL AND MEDICAL 



experiments, most of which were performed by modifica- 

 tions of his technic. He began by immersing embryonal 

 frog tissues in coagulable frog's lymph, taken from the 

 lymph-sac of an adult frog. His studies of nerve cells 

 under these conditions were a brilliant success, for he 

 found not only that it was possible to keep the cells alive 

 and have them multiply, but he was able to see how the 

 cells grew and developed and to demonstrate that the 

 neuraxis is really an outgrowth of a central neuron. 



Harrison and Burrows improved the technic by using 

 plasma of the blood instead of lymph, and in it were able 

 to cultivate tissues of an embryo chick. The plasma was 

 dropped upon a cover glass, the bit of tissue placed in the 

 center of it, and the whole inverted in a hollow-ground 

 slide and kept in a thermostat. By this technic they 

 cultivated bits of the central nervous system, of the heart, 

 and of the mesenchymal tissues. 



Carrel and Burrows took up the pursuit of the subject 

 systematically and showed that by this method and 

 slight modifications of it it was possible to cultivate al- 

 most all of the adult tissues of the dog, cat, chicken, rat, 

 and guinea-pig in vitro. According to their nature the 

 tissues generated connective tissue or epithelial cells 

 which grew in the plasmatic medium either in continuous 

 layers or in radiating chains. They were able to observe 

 direct division of the nuclei during the life of the cells, 

 and the occurrence of many karyokinetic figures in the 

 fixed and stained cultures. The usual duration of the 

 life of a culture was about two or three weeks, but by 

 transplantation they were able to keep the cells alive and 

 growing for a much longer time. 



Rous, using the same methods, was able to keep tissue 

 from a tumor (sarcoma of a chicken) growing in the same 

 way, and Lambert and Hanes did the same with the 

 tissue of a mouse tumor. 



Ruth adapted the method to the study of the process 

 of healing, Carrel and Burrows adapted it to the investi- 

 gation of the effects of internal secretions and other sub- 



