8o 



THE RISE AND FALL OF BACTERIAL POPULATIONS 



either of two different ways. In a moderately favorable medium, such as water, the 

 cycle usually ends with a new level of stability {EF in Fig. i) on which the number of 

 bacteria may remain reasonably constant for an indefinite period. Miquel describes 

 an experiment in which a bottle of Seine River water containing originally 4,800 bac- 

 teria per cubic centimeter was stored for nine years and showed 220 bacteria per cubic 

 centimeter at the end of that time. 



Sometimes, as is shown in Figure 2, there may be one or more secondary waves of 

 increase before the final level of stability is reached. 



In his study of stored feces Jordan (1926) found that after the initial multiplica- 

 tion and subsequent decrease a level was reached which remained more or less con- 

 stant for long periods. The total number of bacteria present after many weeks may be 

 as high as, or higher than, the number initially present. Bact. coli, however, ultimate- 

 ly disappears from the fecal flora under such conditions. In a less favorable medium, 



TABLE X 

 Values of K for Various Periods of Certain Mortality Curves 



on the other hand, the phase of readjustment ultimately ends in complete sterility, as 

 in disinfection with high heat or strong chemicals {EF' in Fig. i). 



In an intermediate case — where conditions are neither sufficiently favorable to 

 permit of the balanced growth and death which maintains a constant stable level nor 

 sufiiciently unfavorable to lead to rapid and complete extinction — a small proportion 

 of the original bacterial population may persist for a very long period. Thus Parkes 

 (1903) was able to isolate typhoid bacilli from blankets soiled with feces after more 

 than six months. Konradi (1904) reports Bact. typhosimi as surviving in water after 

 seventeen months. Robertson (1898) isolated the same organism from moistened soil 

 after eleven months. Studies by numerous observers on the drying of typhoid, diph- 

 theria, and tubercle bacilli (summarized by Chapin, 191 2) have shown that all these 

 organisms may survive drying for several months. (Table X.) 



Winslow and Kligler (1912) found over 51,000 colon bacilli and 42,500 acid- 

 forming streptococci per gram of dust from city streets and 940 colon bacilli 

 and 22,040 acid-forming streptococci per gram of house dust. Winslow and Sanjiyan 

 (1924) conducted an extensive study of the distribution of the acid-forming strepto- 

 cocci, presumably indices of pollution from mouth spray, on objects and surfaces of 

 various kinds. Objects, such as eating utensils, directly exposed to mouth contan? 



