60 BIOLOGY OF DEATH 



lire 14 shows a particularly beautiful nerve fiber prepar- 

 ation made by Burrows. 



The fibers grew from a preparation of the embryonic 

 nervous system of the chick. There can be no doubt, as 

 these figures so clearly show, of the life of these cells 

 outside the body, or of the normality of their develop- 

 mental and growth processes. 



Under the guidance of Harrison, another worker, 

 Burrows, improved the technique of the cultivation of 

 tissues outside the body, first by using plasma from the 

 blood instead of lymph and later in various other ways. 

 He devised an apparatus for affording the tissue culture 

 a continuous supply of fresh nutrient medium. There is 

 in this apparatus a large culture chamber which takes 

 the place of the plain hanging drop in an hermetically 

 sealed cell. On the top of this culture chamber there is 

 a wick, which carries the culture fluid from a supplying 

 chamber and discharges it into a receiving chamber. The 

 tissue is planted among the fibers of the wick, which are 

 pulled apart where it crosses the top of the chamber. 

 The whole system is kept sterile and so arranged that 

 the growing tissue can be kept under observation with 

 high powers of the microscope. The nutrient medium 

 may be modified at will, and the effects of known sub- 

 stances upon the cellular activities of every sort may 

 be studied. 



Burrows began his investigations in this field on the 

 tissues of the embryo chick. With the success of these 

 cultures was established the fact that the tissues of a 

 warm blooded animal were as capable of life, develop- 

 ment, and growth outside the body as were those of cold- 

 blooded animals, such as the frog. Burrows succeeded 

 in cultivating outside the body, cells of the central nervous 



