LOGARITHMIC ORDER OF DEATH 21 



is a most obvious one : with bacteria, the individual is 

 dead when a single cell dies ; with higher organisms, the 

 death of one cell does not kill the organism. It is not 

 known how many cells of any tissue must be killed to 

 cause, e.g., the death of a tadpole or an insect or a plant 

 seed, but it is certain that no single cell is so all-im- 

 portant that its death causes the death of the entire 

 organism. 



The order of death of the individual cells in the 

 tissues of higher plants or animals would be very diffi- 

 cult to ascertain because in most cases it is impossible 

 to obtain cells of equal resistance and to expose them 

 simultaneously. But it seems reasonable that the single 

 cells of tissues should die like the single free-living cells. 



Let us now investigate the order of death by heat in 

 a multicellular organism, such as a tadpole, assuming 

 that there is in that animal a vital organ, for example, 

 the brain, which is most sensitive to heat. The survivor 

 curve of the individual brain cells would be 



("iw") ""(w) ■■■ Ki5r) 



"* ''Tor " 



The probability that a certain definite cell in the brain 

 is still alive after t time units is 



p=(T5(r)' 



and the probability that it is dead is 

 P = l- 



100 



Since s/100 is smaller than 1, (s/100)' decreases rap- 

 idly with longer exposure times. Therefore, the prob- 

 ability that this one cell is dead increases rapidly with 

 prolonged exposure. 



The probability of death of another definite brain cell 

 is the same. The probability that both these cells are 

 dead at the time t is 



