GROWTH 269 



With colonies of Bad. aerogenes, the variability 

 decreased as the size increased. This is due to the fact 

 that fast and slow reproduction is a matter of chance, and 

 not an inherent quality of the individual cell. The more 

 generations we observe, the smaller will be the probability 

 of the average being influenced by chance. 



With mammals, the gestation period shows a relatively 

 small variation, and no asymmetry. 



id) SUMMARY 



Fermentation and respiration is brought about by 

 catalysts (enzymes) of which each cell contains a con- 

 siderable number. They can be regenerated by the cell. 



Multiplication is brought about by very many 

 different catalysts (genes), each cell containing usually 

 only one of each kind. A gene, once lost, cannot be 

 regenerated by the cell. 



The molecules which bring about growth, i.e., synthe- 

 sis, must be arranged in the cell in a definite position 

 to each other to prevent the loss of partly finished build- 

 ing material. 



The enzyme molecules that cause fermentation and 

 liberation of energy must be in a definite position to 

 the growth-producing catalysts to prevent loss of energy 

 by radiation or conduction. 



By making several simplifying assumptions, it can 

 be shown that uniform cells in uniform environment 

 will not all divide at the same time, but must have a 

 definite frequency curve of the growth rate which is 

 asymmetric and askew. The theory demands that the 

 progeny of rapid and of slow growing individuals should 

 have the same average growth rate, and that cells with only 

 a few genes should vary more than those with many genes. 

 All of these demands are borne out by the experiment. 



