46 GENERAL PHYSIOLOGY OF BACTERIA 
30 per cent solution of glucose exerts a pressure of about 22 atmos- 
pheres. A bacterial cell placed in such a solution is under a great 
strain. If bacteria which are in a state of equilibrium with reference 
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} 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 
necessarily 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 Xicolle 
and Auclaire^ 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 quickly increasing the intracellular 
pressure until frequently the cell membrane ruptures, permitting the 
escape of some of the cell contents. This phenomenon is called ylas- 
moptysis.'^ Most bacteria do not plasmoptyze readily, and it is prob- 
lematical how much importance should be attached to either plasmoly- 
sis 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 e\'en 
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 INIeltzer^ 
and others'' have shown that violent shaking gradually kills bacteria; 
not, however, by rupturing the cell membrane. The organisms 
undergo a gradual disintegration, and the injurious effects observed 
are said by these observers to be not purely mechanical. 
' Fisher: Loc. cit., p. 23. 
2 See Phillip: Phys. Chem., 2d ed., 1913, pp. 58, 64 for discussion. 
3 Ann. de I'lnst. Pasteur, 1909, 23, 547. 
* Fischer: Loc. cit., p. 48. 
6 Ztschr. f. Biol., 1894, 30, 464. 
•^ Fliigge: Die Mikroorganismen, Leipzig, 1896, 1, 135, 145, 445, for literature. 
