^y 



V 



INTRODUCTION 



To understand the death of multicellular organisms, it 

 seems necessary to be acquainted with the death of indi- 

 vidual cells. This book deals with the death of single 

 cells, and although bacteria are not in all respects di- 

 rectly comparable with tissue cells, the fundamental 

 principles involved in death are the same. The study of 

 the death of bacteria furnishes, therefore, a solid founda- 

 tion for a general study of death. 



Extensive researches on disinfection and sterilization 

 have resulted in a great deal of detailed information on 

 the death of bacteria. An attempt is made in this book to 

 sort out the experimental evidence and to search for the 

 basic reactions which cause death. 



A study of death should logically begin with a defini- 

 tion of death, but right there, difficulties arise. Death 

 cannot be defined by positive criteria ; it can be character- 

 ized only by the absence of some property which is es- 

 sential to life. But different groups of biologists differ 

 in their views on the most essential properties of liv- 

 ing organisms. The death of a cell is not always de- 

 termined by the same method; the loss of motility, of 

 respiration or of other enzyme activities, the increase in 

 permeability which makes plasmolysis impossible and 

 causes the absorption of dyes, are variously used as 

 criteria of death. These criteria do not always appear 

 simultaneously (Rahn and Barnes, 1933) because, as will 

 be shown, they indicate an inactivation of different cellu- 

 lar mechanisms. Thus, a cell may be alive according to 

 one definition, and dead according to another. 



The bacteriologist has no choice of definition because 

 bacteria are too small to permit an easy study of any of 

 the above criteria. The criterion almost universally used 

 by him to define death is the loss of reproduction. All 

 standard methods used in the study of disinfection and 



