32 BACTERIA 



becoming of the first importance in bacteriology. When 

 species were first isolated in pure culture it was found that 

 they behaved somewhat differently under differing circum- 

 stances. This modification in function has been attributed 

 to differences of environment and physical conditions. 

 Whilst it is true that such external conditions must have a 

 marked effect upon such sensitive units of protoplasm as 

 bacteria, it has recently been proved that one great reason 

 why modification occurs in pure artificial cultures is that the 

 species has been isolated from amongst its colleagues and 

 doomed to a separate existence. One of the most abstruse 

 problems in the immediate future of the science of bacterio- 

 logy is to learn what intrinsic characters there are in species 

 or individuals which act as a basis for the association of 

 organisms for a specific purpose. Some bacteria appear to 

 be unable to perform their regular function without the aid 

 of others. An example of such association is well illustrated 

 in the case of tetanus, for it has been shown that if the 

 bacilli and spores of tetanus alone obtain entrance to a 

 wound the disease may not follow the same course as when 

 with the specific organism the lactic-acid bacillus or the 

 common organisms of suppuration or putrefaction also gain 

 entrance. There is here evidently something gained by as- 

 sociation. Again, the virulence of other bacteria is also in- 

 creased by means of association. The Bacillus coli is an 

 example, for, in conjunction with other organisms, this ba- 

 cillus, although normally present in health in the aliment- 

 ary canal, is able to set up acute intestinal irritation, and 



laboratories and in disinfecting apparatus moist heat is invariably preferred to 

 dry heat. For with the latter such high temperatures would be required that 

 they would damage the articles being disinfected. Koch states the following 

 figures for general guidance : Dry heat at a temperature of 120 C. (248 F.) 

 will destroy spores of mould fungi, micrococci, and bacilli in the absence of 

 their spores ; for the spores of bacilli 140 C. (284 F.), maintained for three 

 hours, is necessary ; moist heat at 100 C. (212 F.) for fifteen minutes will kill 

 bacilli and their spores. 



