184 Harvey. — The Action of Poisons upon 
The above equation is the same as that for a unimolecular chemical 
reaction, if is the active mass after time and n 2 is the active mass after 
time t 2 . A bimolecular chemical reaction in which one active mass is in 
great excess approximates in velocity to a unimolecular reaction. The same 
equation as the above was arrived at by Madsen and Nyman, and indepen- 
dently by Miss Chick 1 in 1907, for the rate of disinfection of bacteria. 
Results of a similar nature have been obtained by Dr. F. F. Blackman 2 
and Miss N. Darwin for the death-rate with higher plants. 
TABLE II. 
Strength of hydrochloric acid = -009 per cent. 
Time in 
mins. 
Number fallen in 
two experiments. 
Number 
surviving 
1 . n x 
log = 
t^-h 6 n , 2 
0 
2+1= 3 
113 
5 
19 + 28= 49 
67 
(0.045) 
10 
34 + 52= 86 
30 
0.070 
15 
39 + 63=102 
14 
0.066 
20 
45 + 65=110 
6 
0*074 
25 
49 + 65 — 1 13 
3 
0*060 
30 
51 + 65 = 116 
0 
35 
51 + 65= 116 
/ 0 
Miss Chick points out the analogy between the death-rate of bacteria 
and the rate of decomposition of molecules of a chemical compound ; as, 
for instance, those of cane-sugar undergoing hydrolysis in a weak acid 
solution. The same analogy applies to the relations between the death- 
rate and the concentration of the poison, and between the end point of 
a bimolecular reaction and the concentration of the active substance in 
excess. An explanation has been given for the rate of a chemical reaction 
to the effect that ‘ at a particular time only a proportion of the molecules 
are temporarily in such a state as to permit of the combination \ The 
same explanation seems to apply to the reaction between a poison and 
cells of bacteria and Chlamydomonas . 
The death of the cells might be expected to occur after a fixed pro- 
portion of one or more substances in the protoplasm had decomposed, but, 
although the rate of decomposition of such a substance or substances would 
follow a logarithmic curve obeying the above equation, the time for death 
to take place would depend upon the quantity of such substances in the 
individual cells, and upon the proportion necessary to be decomposed before 
death took place. Why the cells of bacteria and Chlamydomonas behave 
in this way, like the molecules of a chemical compound, has yet to be 
explained. 
1 Harriette Chick : Journal of Hygiene, Jan. 1908. 
2 British Association, Sept. 1908. 
