40 LOGARITHMIC ORDER OF DEATH 



tion of a very few molecules but if this number is higher 

 than 4 or 5, the order is very definitely not logarith- 

 mic. This eliminates denaturation of enzymes or of the 

 cytoplasm as the cause of death, wherever the logarith- 

 mic order prevails, because it does not seem possible that 

 inactivation of a very few of the numerous identical mole- 

 cules can kill the organism. It would probably exclude 

 also the disruption of the cell membrane as a cause of 

 death, for this is likely to require inactivation of a con- 

 siderable number of molecules before damage becomes ir- 

 reparable. 



Let us now consider the bacteriologist's definition of 

 death : a bacterium is dead when it has lost the power to 

 reproduce. Cell division is linked with chromsome di- 

 vision, the chromsomes contain the genes, and the inac- 

 tivation of certain genes is known to cause ''lethal muta- 

 tions," i.e., to prevent the cell from multiplying. While 

 chromsomes and genes have not been definitely found in 

 bacteria, these organisms undoubtedly have some heredi- 

 tary mechanism, and hereditary units. As a rule, there 

 are two genes of the same kind in a diploid cell, and one 

 in a haploid cell. According to Fricke and Demerec 

 (1937): "we may assume that a gene contains about 

 2500 atoms . . . This would indicate an average gene di- 

 ameter of about 25 A." This is the size of a quite small 

 protein molecule. A gene, then, would consist of only 

 one or two molecules. Each gene is ditferent from all 

 others, and has its own rate of denaturation. If one vi- 

 tally essential gene is denatured, and the cell can no 

 longer divide, the bacterium is sterile, that is, dead, ac- 

 cording to the bacteriological definition. 



This explanation, namely, that ''death" of bacteria is 

 brought about by the inactivation of a gene (Rahn, 1929, 

 1934) is correct only for the bacteriologist's definition 

 of death. Jordan (1940) defined the death of bac- 

 teria as "lethal mutation." The very extensive data on 

 mutations brought about by X-rays, and on the lethal ef- 



