22 Plant Tissue Culture 



juice or their equivalents (Burrows, 1910, 117, 

 118, 1911, 119; Carrel, 1911, 120, 1912, 121-125, 

 1913, 190; Carrel and Burrows, 1910, 128). The 

 method outlined in 1913 by Carrel (Fig. 9) has 

 changed only in minor details since that date. 



Carrel and Burrows ' method of cultivating ani- 

 mal cells in a blood-plasma embryo-juice nutrient, 

 while relatively simple and easily duplicable, has 

 not led to any exact knowledge of the nutrient 

 requirements of such cells and tissues. Blood 

 plasma and embryo juice are organic complexes 

 of unknown constitution, and such attempts as 

 have been made to elucidate their makeup have not 

 been especially successful (Baker, 1929, 233, 1933, 

 183; Baker and Carrel, 1925, 195, 1926, 184, 185, 

 1927, 186, 1928, 187-189 ; Carrel and Baker, 1926, 

 191 ; Ebeling, 1921, 192 ; Fischer and Demuth, 1928, 

 194). Nor have the attempts at a synthesis of a 

 nutrient, led by Dr. and Mrs. Warren H. Lewis 

 (Figs. 7, 8) in this country and Dr. A. H. Drew in 

 England been much more successful in eliminating 

 the unknowns (Baker, 1936, 234; Drew, 1922, 145, 

 1923, 146 ; M. E. Lewis, 1916, 148 ; M. R. and W. H. 

 Lewis, 1911, 149-151, 1912, 152, 153 ; W. H. Lewis, 

 1921, 154, 1923, 155, 1929, 156; Vogelaar and 

 Erlichmann, 1933, 162, 1934, 163, 164, 1936, 235, 

 1937, 236, 1939, 165). The cultivation of animal 

 tissues is still an empirical science. 



