48 GENERAL PHYSIOLOGY OF BACTERIA 



to the osmotic pressure of a solution are suddenly introduced into 

 media containing a greater concentration of solutes, the contents of 

 the cell diminish somewhat in amount, due to the rapid withdrawal of 

 water leaving the rigid cell membrane visible. This shrinkage of the 

 cell contents is spoken of as plasmolysis. 1 This shrinkage of the cell 

 contents would indicate that the cell membrane is differentially more 

 rapidly permeable to water than to crystalloids. All bacteria are not 

 plasmolyzed when they are suddenly introduced into hypertonic 

 solutions, and some organisms exhibit the phenomenon of plasmo- 

 lysis to a much greater extent than others. Plasmolysis does not neces- 

 sarily result in the death of the organism. It appears to be a fact that 

 older bacteria are frequently more readily plasmolyzed than younger 

 individuals of the same kind. The observations of Nicolle and Auclaire 2 

 would indicate that bacteria which retain the Gram stain are less 

 readily plasmolyzed than Gram-negative bacteria. Whether Gram- 

 positive bacteria which have become Gram-negative due to prolonged 

 cultivation in artificial media invariably follow the same rule is not 

 known. 



If bacteria are gradually subjected to solutions of greater or lesser 

 osmotic pressure, they usually accommodate themselves to these 

 changes without visible effect. If bacteria are introduced abruptly 

 into solutions of low osmotic pressure or distilled water, water rapidly 

 passes through the cell membrane of the bacteria faster than the solutes 

 within the cell can pass out, thus rapidly increasing the intracellular 

 pressure until frequently the cell membrane ruptures, permitting the 

 escape of some of the cell contents. This phenomenon is called 

 plasmoptysis. 3 Most bacteria do not plasmoptyze readily, and it is 

 problematical how much importance should be attached to either 

 plasmolysis or plasmoptysis in practical bacteriology. 



3. Agitation. Bacteria grow best in quiet surroundings, although 

 a slight amount of agitation is usually harmless and may be even 

 beneficial if it tends to dislodge waste products from the immediate 

 surroundings of sedimented organisms. Rapid agitation frequently 

 retards the multiplication of bacteria in fluid cultures, and Meltzer 4 

 and Horvath 5 have shown that violent shaking gradually kills bacteria; 

 not, however, by rupturing the cell membrane. The organisms undergo 



1 Fischer, loc. cit., p. 23. 



2 Ann. de 1'Inst. Pasteur, 1909, xxiii, 547. 



3 Fischer, loc. cit., p. 48. 



4 Ztschr. f. Biol., 1894, xxx. 

 6 Pfliiger's Arch., 1887, xvii. 



