PART D 



MECHANISM OF DEATH 

 I. DEFINITIONS OF A DEAD CELL 



Death has been defined in the introductory chapter as 

 a function by itself; it consists not merely in the absence 

 of fermentation and growth, but is a chemical process. 

 We might perhaps define it more accurately by saying 

 that dying is a chemical process which becomes irreversi- 

 ble after a while; from this time onward, the cell is 

 considered dead. 



The customary conception of dead bacteria is that they 

 can not grow on the agar plate, nor in broth; in other 

 words, that they have permanently lost the power of 

 reproduction. This definition is different from those 

 of other biological sciences; it is distinctly a bacteriologi- 

 cal one. Cells which have lost the power to reproduce 

 may still ferment; their protoplasm may still appear 

 normal under the microscope, and may still be capable of 

 plasmolysis. Such cells would be considered alive by 

 most biologists. 



It may be well to realize from the very beginning that 

 many definitions of a dead cell exist which might give 

 cause for considerable confusion unless their meaning 

 is kept in mind all the time. 



The bacteriological definition is not more exact than any of the 

 others, as may be seen from the experiments of Supfie and Dengler 

 (1916) who dried anthrax spores on silk threads, heated them in 

 steam for various lengths of time, and then placed each thread in 

 broth. They took dupUcate samples, and tested one in standard 



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