34 BACTERIOLOGY 



circumstances, e.g. with a suitable food-supply, temperature, 

 etc., this division may occur on the average about once in 

 twenty to thirty minutes, so that, if there were no factors 

 acting to delay or prevent such multiplication, a single 

 organism would give rise, in the course of some ten hours, to 

 a progeny of a couple of millions, or, in twenty-four hours, to 

 the inconceivably huge number of 75,000,000,000,000 offspring ! 

 Fortunately, however, Nature interposes many checks and 

 barriers to restrict this unlimited multiplication for, if she 

 did not, there would be room for nothing but bacteria on the 

 face of the earth. Chief among such barriers are limitation 

 of the food-supply, and the production by the bacteria them- 

 selves of excretions and by-products which hinder or inhibit 

 their further multiplication. Thus in alcoholic fermentation 

 there is active proliferation as long as there is plenty of the 

 sugar or other substance for the bacteria to feed upon, and 

 also until the alcohol and other products of their activity are 

 produced in sufficient amount and concentration to automati- 

 cally stop the process. 



There is also the opposition of other living creatures, for 

 many lowly forms of life, e.g., among the Protozoa, prey upon 

 and devour bacteria for food. In the bodies of the higher 

 animals there are also forces of opposition to the attack and 

 multiplication of bacteria, which will be described in our 

 Chapter on Immunity (p. 42). 



Not only so, but, even in favourable circumstances, the rate of 

 bacterial production is not mathematically constant. There is 

 usually a short period of slow growth whilst initial difficulties are 

 being overcome and the organism is accustoming itself to its 

 surroundings. Then, if these are successfully overcome, there 

 is a varying period of rapid and active proliferation, which, 

 unless the surroundings and food-supply are renewed, gives 

 place to a stationary period, and then, after a varying time, 

 to the decline and ultimate death of the bacteria. This process 

 in many ways resembles what is seen in the growth, decline, 

 and extinction of, say, a nation of human beings, if restricted 

 to a limited area, though here, of course, other higher laws 

 also come into play. Some races of bacteria are much more 

 resistant than others. Some can live and be grown only 

 with the greatest difficulty upon artificial media dying off, 

 perhaps in a few hours or days. Others are very hardy, and 

 can live, for example, in a culture-tube, for months and even 

 years. Some, again, have developed special methods of resist- 

 ing adverse conditions. This is notably the case with those 

 organisms which form spores, such as the bacilli which cause 

 Anthrax (" Splenic Fever " of cattle), Tetanus or Lockjaw, and 



