LOGARTTHMTC ORDER OF DEATH 41 



fects of X-rays, all point very definitely to the fact that 

 the genes are the most sensitive part of the cell. Fre- 

 quently, while no other effects of irradiation are immedi- 

 ately noticeable on the irradiated plants or animals, ster- 

 ility has been induced, or, when the affected genes are 

 less essential, the offspring is abnormal in some way. 



To this mass of indirect evidence has recently been 

 added the chemical production of mutants in fungi. Thom 

 and Steinberg (1939) obtained stable mutants of several 

 Aspcrgilli by making the spores germinate on agar 

 containing KNO,. All mutations consisted in the loss 

 of some activity related to the reproductive function, and 

 have been explained by the authors as being caused by 

 inactivation of some amino groups in one of the genes. 



Analogous findings have been recorded in bacteria. 

 Penfold (1911) grew Bacterium coli on agar containing 

 chloracetate ; among the few bacteria that survived, were 

 some which had permanently lost the power to produce 

 gas from glucose. Eevis (1912) obtained the same re- 

 sult with malachite green and brilliant green. Lom- 

 mel (1926), by means of weak disinfectants, produced a 

 variant of Bacterium coli which had lost the ability to fer- 

 ment lactose. Unpigmented "albino" strains of Bacte- 

 rium prodigiosum can be obtained by cultivation at very 

 high temperature. All the mutations cited were irrever- 

 sible. If, in bacteria and fungi, weak disinfectants can 

 permanently inactivate some genes, which control fer- 

 mentation, reproduction or pigmentation, it is highly 

 probable that, in general, they cause changes in genes nec- 

 essary for life and thereby produce sterile mutants, 

 which the bacteriologist would consider dead. 



