The Origin of Life 31 



as we speak of the immortality of the germ cells of such 

 animals. x 



This view receives its support first from the fact that 

 certain trees like the Sequoia live several thousand years 

 and may therefore be considered immortal ; and second, 

 from the method of tissue culture. The method of 

 cultivating tissue cells in a test tube, in the same way 

 as is done for bacteria, was first proposed and carried 

 out by Leo Loeb, in 1897, 2 but his test-tube method 

 did not permit the observation of the transplanted cell 

 under the microscope. This was made possible by a 

 modification of the method by Harrison, who established 

 the fact that the axis cylinder grows out from the gan- 

 glionic cell. Harrison and Burrows then perfected 

 the method for the cultivation of the cells of warm- 

 blooded animals, and with the aid of these methods 

 Carrel succeeded in keeping connective-tissue cells 

 of the heart of an early chick embryo alive more 

 than four years, and these cells are still growing 

 and dividing. 3 Only very tiny masses of cells can 

 be kept alive in this way since all the cells in the 

 centre of a piece die on account of lack of oxygen; 



1 Loeb, Leo, Jour. Med. Res., 1901, vi., 28; Arch. f. Entwicklngsmech., 

 1907, xxiv., 655. 



2 Loeb, Leo, Uber die Entstehung von Bindegewebe, Leucocyten und 

 rothen Blutkorperchen aus Epithet und ilber eine Methode isolierte Gewebs- 

 teile zu zuchten. Chicago, 1897. 



3 While this has been demonstrated thus far only for connective- 

 tissue cells it may be true also for other cells. 



