上游充通大￥ Shanghai Jiao Tong University Figure 6.17 Counting bacteria by filtration.(a)The bacteria in 100 ml of water were sieved out onto the surface of a membrane filter.(b)Such a filter,with the bacteria much more widely spaced, was placed on a pad saturated with liquid nutrient medium,and the individual bacteria grew into visible colonies.One hundred twenty four colonies are visible,so we would record 124 bacteria per 100 ml of water sample. Bacteria can be counted by filtra- tion when their quantity is very small. (b) (a) SEM 2um 1 陈峰，上海交通大学生命学院微生物学Shanghai Jiao Tong University 陈峰，上海交通大学生命学院微生物学