20 LOGARITHMIC ORDER OF DEATH 



II. ORDER OF DEATH IN MULTICELLULAR VERSUS 

 UNICELLULAR ORGANISMS 



The difference in the order of death between bacteria 

 and higher organisms has occasionally been questioned.* 

 A survey of all experiments on the order of death in 

 bacteria until 1930 (Rahn, 1931) showed that 25% of 

 the curves resembled those of multicellular organisms, 

 21% were strictly rectilinear, and 54% were concave 

 upward, like that of Figure 3. Most of the 25% re- 

 sembling multicellular organisms were actually obtained 

 with ''multicellular" bacteria, i.e., the bacteria were clus- 

 tered as will be explained in more detail on p. 42. Since 

 that survey a number of new investigations have veri- 

 fied the logarithmic order, e.g., the extensive investiga- 

 tions by Watkins and Winslow (1932), and by Beamer 

 and Tanner (1939a and 1939b). Only two authors, both 

 working with chlorine, have obtained survivor curves 

 which are consistently concave downwards. It cannot be 

 doubted any more that the majority of disinfectants, 

 as well as heat and irradiation, result in an order of 

 death in bacteria which is quite different from that of 

 higher animals and plants. 



The difference between bacteria and higher organ- 

 isms which causes this difference in the order of death 



*In the case of death by irradiation no mortality data comparable 

 to those obtained with other killing agents could be found in the 

 literature for higher organisms. The order of death is frequently given 

 in experiments with ultra-violet and X-rays, but the signification of 

 these data is different from that of other experiments. Irradiated 

 organisms appear normal for a long time after they have received a 

 lethal dose. The zero time for them is the moment when irradiation 

 ceased, while, in all other experiments, it is the moment when exposure 

 begins. If an insect, for example, does not die until a week after it 

 received the lethal dose, it is clear that time-mortality curves mean 

 very little. 



This point is important in the study of the ultimate mechanism of 

 death. Evidently, If a plant or animal survives for days after it has 

 received a lethal dose, it is not the destruction of its enzymes and 

 cytoplasm which is responsible for its death. Yet, the organism dies. 

 Some irreparable damage has been done to some cell function which 

 is not immediately needed. The similarity of this phenomenon Avith 

 the fact that irradiated gonads often produce normal-appearing animals 

 which, however, are sterile, suggests that death by irradiation is due 

 to the inactivation of some genes. 



