MECHANISM OF DEATH 337 



of growth and death problems difficult to analyze. 

 There are, in the general technique of disinfection 

 experiments, two distinct methods of procedure which 

 give different results; the one is to remove the bacteria 

 from the poisonous solution, usually together with a 

 small part of the solution, and put them into broth or 

 agar without any further treatment; the other is to 

 remove by chemical or physical means any traces of the 

 poison from the outside and inside of the cells as far as 

 that is possible, i.e., as far as the poison has not formed 

 irreversible compounds with the cell contents. 



The first method is rather unsatisfactory inasmuch as the amount 

 of poison transferred to the medium for cultivation of the survivors 

 is not always the same. While the amount is not sufficient to prevent 

 growth of healthy cells, it might prevent recovery of injured bacteria. 

 A method of merely physical removal is sometimes used by trans- 

 ferring the cells from the disinfectant into water, centrifugalizing 

 them off and eventually repeating the washing before placing them 

 into the test medium. In this way, all soluble poison is removed 

 from the outside and the inside of the cell, but chemical combinations 

 of the poison with cell contents remain unchanged. 



If the viability tests on culture media are supposed to correspond 

 with the viability in the animal, the poison must be removed 

 completely by chemical means. The tissue around the wound in 

 which the treated bacteria are placed has a tendency to remove the 

 last traces of poison from within the bacterial cell, and at the same 

 time, it is a very good medium for growth. This is shown very 

 clearly in some experiments of Rodewald (1923). The bacterium of 

 fowl cholera was placed in 0.1% HgCh, removed after certain time 

 intervals, and washed four times in succession with 40 c.c. of water. 

 After seven minutes' treatment with HgCl2, the washed bacteria 

 showed no more growth on sterile culture media, but when injected 

 into mice, killed them; even those Which had been in the bichloride 

 for three hours, still caused the disease. Similar results were 

 obtained with phenol. 



The action of the living tissues is perhaps partly due to their 

 being an excellent food, but quite likely, their adsorptive properties 



