36 THE STORY OF GERM LIFE. 



third period it is a simple mass of spherical 

 spores. A spherical form, when it lengthens 

 before dividing, appears as a short rod, and a 

 short rod form after dividing may be so short as 

 to appear like a spherical organism. 



With all these reasons for confusion, it is not 

 to be wondered at that no satisfactory classifica- 

 tion of bacteria has been reached, or that differ- 

 ent bacteriologists do not agree as to what consti- 

 tutes a species, or whether two forms are identical 

 or not. But with all the confusion there is slowly 

 being obtained something like system. In spite 

 of the fact that species may vary and show 

 different properties under different conditions, 

 the fundamental constancy of species is every- 

 where recognised to-day as a fact. The members 

 of the same species may show different properties 

 under different conditions, but it is believed that 

 under identical conditions the properties will be 

 constant. It is no more possible to convert one 

 species into another than it is among the higher 

 orders of plants. It is believed that bacteria 

 do form a group of plants by themselves, and 

 are not to be regarded as stages in the history 

 of higher plants. It is believed that, together 

 with a considerable amount of variability and 

 an occasional somewhat long life history with 

 successive stages, there is also an. essential con- 

 stancy. A systematic classification has been 

 made which is becoming more or less satisfactory. 

 We are constantly learning more and more of the 

 characters, so that they can be recognised in 

 different places by different observers. It is the 

 conviction of all who work with bacteria that, in 

 spite of the difficulties, it is only a matter of time 

 when we shall have a classification and descrip- 



