156 Plant Tissue Culture 



proteins themselves, but, if we set aside all con- 

 stituents of an organism except protein and fol- 

 low the increase or decrease in this one constitu- 

 ent, we have about as good a measure of the 

 increase or decrease in living substance under a 

 given set of conditions as is at present available. 

 This can be done by aliquot determinations of non- 

 soluble amino-nitrogen. Mueller recognized this 

 when he chose this criterion as the only acceptable 

 one in the measurement of growth of diphtheria 

 bacilli under the influence of different nutrient 

 complexes (Mueller, 1935, 176). 



The actual measurement of amino-nitrogen, 

 while slow and tedious, is not especially difficult. 

 It could be applied to tissue culture practice as a 

 routine procedure, if desired. It has, however, 

 one very serious drawback which, together with 

 its tediousness, has prevented its coming into 

 common practice. This is the fact that it requires 

 the destruction of the material measured. In 

 studying living, growing organisms, this is a seri- 

 ous drawback, since it prevents the making of sub- 

 cultures from examples which prove to be espe- 

 cially favorable. The best that can be done is to 

 make such measurements on a series of aliquots, 

 using sufficient numbers so that the results will 

 truly represent the characteristics of the whole 

 series. This method easily becomes cumbersome 

 or unreliable, or both. 



