74 MILK [vi 



points are worthy of note. For one thing, it may 



take place at an enormous rate. A bacterium may 



develop in twenty minutes' time the power of repro- 



ducing itself, so that under favourable 



9 o% 9 circumstances, in a few hours' time, 



it may give rise to a progeny number- 



FIQ.H.-MICROCOCCI, i millions. Indeed, according to 



SHOWING MODE OF 



MULTIPLICATION BY Conn, the microbes descended from 



FISSION. (Frank- 

 land.) a single individual, if permitted to 



develop under the most favourable circumstances, 

 would, in less than five days, occupy a space equal to 

 that of the entire ocean. It is needless to say that 

 such favourable circumstances never do exist. 



Again, with regard to spores, it has been found 

 that they possess very much greater powers of re- 

 sistance than the developed 

 bacterium. The greater vital- 

 ity possessed by the spores, 

 in comparison with the adult 

 cells, is due to the harder 

 nature of the covering mem- 



i mi i J_.L 1 nu. iz. iriuLTii'ijUjAriujN to 



brane. The latter is, as a rule, SPORES OF BACILLI. (Frank 

 comparatively easily killed by land>) 

 unfavourable circumstances, but the former in some 

 cases possess extraordinary powers of resistance. 



Size of Bacteria. The size of bacteria is so minute 

 that they require a high power of the microscope to 

 distinguish them. They are only visible to the 



to 



FIG. 12. MULTIPLICATION BY 



