PART C 



GROWTH 



I. GENERAL CONSIDERATIONS 



(a) MEASUREMENT OF GROWTH 



Growth, here, shall be understood to mean the total 

 increase of the cell substance of living matter. No 

 distinction will be attempted between the two processes 

 comprised in the increase in size of one cell, and the 

 splitting of this enlarged cell into two smaller cells. It 

 would clear up matters if such distinction could be made, 

 but it cannot, as the factors concerned in the process of 

 cell division have not, as yet, been approached by chemical 

 analysis. All we may do is measure growth by the 

 increase in total weight or volume of living matter, or by 

 counting the increase in the number of cells, with the 

 assumption that the newly grown cells weigh as much 

 in the average as the ones at the start. We know that 

 the young and old cells differ in volume (Henrici, 1928), 

 but we know nothing about their moisture contents. 



Other indirect methods have been used to measure 

 growth. Rubner (1906a) determined the nitrogen con- 

 tent of the bacteria as a measure of the '^crop,'' and in 

 one experiment, even the sulphur content of the cells 

 was taken as the measure. Turbidity has been used to 

 estimate the number of bacteria (Strauss, 1929), and 

 so has the volume of the cells obtained by centrifugation 

 (Richards, 1928). 



None of these methods gives an absolutely correct conception 

 of the increase of living matter. Nor can any method be suggested 



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