48 J. J. NORTHROP VOL. 12 (iQSS) 



Woods and Trim^^ found the same result for deaminase of C. welchii. 



Price^^ found that the protein, RNA and DNA per cell (staphylococcus) remained 

 constant during log growth. 



Constant ratio of P/B during log growth of lysogenic megatherium was found by 

 Clark and Cowles^^. 



The reverse of this condition is also true. If any cell component or product of 

 metabolism is found to change its concentration relative to any other compound during 

 the steady state of the culture, then a new type of cell must have appeared. 



Hinshelwood^'' has pointed out that such extreme synchronization of reaction 

 rates could hardly exist without some common regulating mechanism. He has shown that 

 a series of reactions, each one dependent on the preceding, can furnish such a regulatory 

 mechanism. 



The derivation of all the substances used in cell synthesis, from a common precursoi 

 by a series of simultaneous reactions (Northrop^^) also leads to synchronization of 

 reaction rates. If any substance in the cells increased at a faster rate than the cells, no 

 matter how slight, sooner or later the cell must be destroyed, while if it increased at a 

 slower rate, sooner or later the last molecule would be lost and a new kind of cell appear, 

 which contained none of the slow growing component*. Loss of plastids by plant cells, 

 or of the Kappa particle of paramecium occur in this way and the loss of phage by lyso- 

 genic bacteria has been reported. The destruction of a cell by overgrowth of a component 

 occurs when a susceptible cell is infected with phage. 



It follows that any cell component which increases in amount per cell in passing 

 from the resting cell to the log growth cell, must decrease in amount again as thecell 

 returns to the resting stage ; otherwise the cycle would not be complete. 



The best conditions, therefore, for comparing various cultures growing in the same 

 media, or the effect of various media on the growth of one culture, is during the 

 "steady state". 



4 



experimental procedure 



Phage determination — 0.2 ml suspension added to 1.8 ml ice cold normal saline and centrifuged 

 at once for 10 min at 3500 R.P.M. Phage determined in supernatant as previously described 

 (NoRTHROp22). Control experiments showed that this procedure stopped phage production as soon 

 as the cells were added to the cold normal saline and did not change the amount of the free phage. 



Cell count — (NorthropI^). 



Protein and RNA — Sample removed from tube and i/io volume of formahn added. Suspension 

 centrifuged, precipitate stirred up with 10 ml cold normal saline, centrifuged. Precipitate washed 

 once more with normal saline and then washed 3 times with cold 5% trichloracetic acid. The rest of 

 the determination was carried out as previously described (Northrop^®). 



Control experiments showed that the RNA and protein content of the cells was not changed 

 by the formalin. 



SUMMARY 



1. The changes in the concentration of cells, free phage, cellular protein, and cellular RNA have 

 been determined during the growth of cultures of lysogenic megatheviuni 899a, in peptone medium. 



2. During the lag phase the RNA increases more rapidly than the cells, and the free phage much 

 more rapidly. 



* All autocatalytic equations express the paradox that, if none of the proiluct formed is present,, 

 none can be formed. This difficulty may be circumvented by assuming that there is another, possibly 

 very slow, reaction which results in the formation of the same product. In the case of the trypsinogen- 

 trypsin reaction this secondary reaction is known to occur. 



References p. 50. 



