102 CHEMISTRY OF BACTERIA AND THEIR PRODUCTS 



the one in which it has been, the cell contents shrink away from the cell 

 wall {plasmolysis) indicating that there exists a semipermeable mem- 

 brane through which water passes more rapidly than salts. If the 

 change in osmotic pressure is gradual, the bacteria accomodate them- 

 selves to it by the slow diffusion of the salts through the cell membrane, 

 indicating that it is not absolutely semipermeable. Different bac- 

 teria behave differently, some bacteria not being plasmolyzed by 

 solutions that plasmolyze others. As a rule, old bacteria plas- 

 molyze more rapidly than young, and in some varieties there seems to 

 be a spontaneous plasmolysis, to which has been attributed the irregular 

 staining of diphtheria and tubercle bacilli, the polar staining of plague 

 bacilli, etc. Plasmolysis occurs only in living bacilli, but does not nec- 

 essarily cause death. The Gram-staining bacteria cannot generally 

 be plasmolyzed, and contain more water. ^ 



When bacteria pass from solutions of higher osmotic concentration 

 into solutions of lower concentration, the phenomenon of plasmoptysis 

 is produced. The cell contents swell until the cell wall gives way at 

 some point, and then exude as glistening drops, which may become 

 detached from the wall and escape free into the fluid. Plasmoptysis 

 is shown best by bacteria that have been grown on salt-rich media 

 before being placed in the salt-free fluid. Not all varieties of bacteria 

 can be made to undergo this change, depending probably upon the 

 degree of permeability of their cell membranes for salts. The ex- 

 posure of the naked cell contents to the hypotonic fluid outside the 

 cells makes plasmoptysis more serious for bacterial life than plasmo- 

 lysis, but how often, if ever, either process plays a part in the resistance 

 of infected animals against bacteria is unknown. The resistance of 

 bacteria to direct pressure is striking; spore bearers may not be killed 

 under direct pressure of 12,000 atmospheres for 14 hours, and non- 

 spored bacteria resist 3,000 but not 6,000 atmospheres.^ 



Chemotaxis.^ — Just as with unicellular animal organisms, bacteria 

 respond to chemotactic influences, in general being attracted bj'' sub- 

 stances favorable for food, such as peptone, amino acids, ^ dilute potas- 

 sium salts, etc., and being repelled by harmful substances, such as 

 strong acids and alkalies. Attempts have been made to separate 

 different organisms in mixed cultures by means of their response to 

 chemotaxis, but without striking success. It is possible that chemo- 

 taxis may play a part in the localization of bacteria from the blood 

 stream in favorable localities, just as leucocytes arc attractd to points 

 of injury, but this has not been demonstrated. (The chemotactic 

 influence of bacteria upon leucocytes is discussed in Chapter xi.) 



3 Nioolle and Alilairc, Ann. Inst. Pasteur, 1009 (23), 547. 

 *Larfc'on, Hartzell and Diehl, Jour. Infect. I)is., lOlS (22), 271. 

 ^ Concerning the adsorption of l)acteria sec Bechhold, Kolloid-Zcitsrhr., 1918 

 (23), 35. 



" Pringsheiin and Ernst, Zcit. pliysiol. Clieni., 19U) (97), 17(). 



