256 THE POWER OF RESISTANCE TO EXTREMES 



spores have typically great resistant powers, although it is not known whether 

 they retain their vitality as long as some seeds do. The properties of bacteria 

 are largely influenced by the cultural conditions and by the stage of development, so 

 that the dissimilar results obtained by different authors with regard to the duration 

 of vitality are readily comprehensible. 



Various species of Spirillum, including Spirillum undula, are at once killed 

 by drying. The same applies to Bacillus carotarum, whose spores, however, resist 

 desiccation *. Kurth 2 found that the rod-like forms of Bacterium Zopfii were killed 

 after two to five days' drying, and the coccus forms after seventeen to twenty-six days. 

 When dried Spirillum cholerae asiaticae dies in from fifteen minutes to a few hours, 

 whereas the typhus, tubercle, and diphtheria bacilli withstand desiccation for weeks 

 or even months. Naturally only those bacteria which are resistant to desiccation 

 at some stage of development can be spread by the air. 



SECTION 71. Osmotic Agencies. 



Every plant will ultimately die if its percentage of water is kept so 

 low as to prevent growth, either by transpiration or by immersal in saline 

 solutions. The specific resistance of different plants varies greatly, however, 

 for many plants are unable to grow in solutions isosmotic with from i to 2 

 per cent, sodium chloride solutions, whereas growth only ceases in others 

 when the concentration is equivalent to from 17 to 20 per cent, of sodium 

 chloride. 



Even when the salts themselves are injurious, the action of a saline 

 solution is not necessarily the same as when a corresponding diminution of 

 turgor is produced by transpiration. In the latter case no plasmolysis is 

 produced with its attendant consequences, and further the sudden change to 

 a saline solution may act injuriously or even fatally upon plants which can 

 withstand air-drying. 



Various algae and fungi can withstand gradual transference from 

 concentrated to dilute solutions, whereas sudden dilution causes the cells to 

 burst owing to their high osmotic pressure. A sudden rise of concentration 

 appears to produce the same effect upon bacteria and infusoria, owing to 

 an excessive and disproportionate rise in their internal osmotic pressure. 

 Thus Fischer 3 has shown that Bacillus ant/iracis, B. coli, B. cholerae die in 

 ten minutes to an hour when suddenly transferred from 0-75 per cent, 

 solutions to 2 per cent, solutions of sodium chloride, although they are able 

 to grow in solutions of 5 to 7 per cent, concentration. To produce this 

 result no plasmolysis need be caused, but the origin of the internal rise of 

 pressure is unknown. 



1 Koch, Bot. Ztg., 1888, p. 298. 2 Kurth, Bot. Ztg., 1883, p. 409. 



3 Fischer, Zeitschr. f. Hygiene u. Tnfectionskrankheiten, 1900, Bd. xxxv, p. 10. Massart 

 (Archives d. Biol., 1889, T. IX, p. 547) states that bacteria may be killed when chemotactically 

 attracted to a solution to which they can be gradually accommodated. 



