LIFE CYCLES OF BACTERIA 09 
satisfactory one has been developed. Much more data may have to be 
secured with regard to the life histories of the bacteria. 
Bacteriological Groups. The arrangement of bacteria into physio- 
logical groups have been carried out merely for convenience. In 
some instances probably these groups are made up of very closely 
related organisms; in other cases a too insignificant characteristic 
has been taken as the standard. The first five groups of Fuller and 
Johnson’s classification of water bacteria have been made on the basis 
of chromogenesis. Jordan also used this same characteristic when he 
systematized the bacteria which he isolated from the Illinois river.’ 
Rahn states, in Marshall’s Microbiology, that this is a convenient and 
helpful method for handling the bacteria. As mentioned above many 
of the groups are arbitrary and often depend upon characteristics 
which are not fixed. Many of the groups need to be subjected to 
careful study. This will tell whether the groups approach natural 
units and, if they do, the relation and characters of the members. 
The groups of pathogenic bacteria and those which have sanitary 
significance have received careful study. 
Life Cycles of Bacteria. It has been the custom in bacteriology to re- 
gard bacteria as monomorphic. So firmly rooted has this idea become 
that few bacteriologists have given thought to the possibility of there 
being life cycles through which the bacteria pass. Involution form has 
been the term which has been applied to many of the forms which were 
regarded as “ abnormal.” In many cases these were explained as con- 
taminations and the culture discarded. That bacteria may possess more 
or less intricate life cycles has been proposed by different workers. 
When the data from these different sources are compared, one is im- 
pressed with the possibility that bacteriologists have been too hasty in 
excluding all of these abnormal forms. Léhnis (1916) has given this 
subject most intensive study. Some of the’ conclusions which this in- 
vestigator has reached are as follows: 
“ A comparative study of 42 strains of bacteria has shown that life 
cycles of these organisms are not less complicated than those of other 
microorganisms. As representatives of all groups of bacteria have been 
tested and all, without exception, behaved essentially in the same 
manner, in all probability analogous results may be expected with all 
species of bacteria. All bacteria live alternately in an organized and 
in an amorphous stage. The latter has been called the “‘ symplastic”’ 
stage because at this time the living matter previously inclosed in 
the separate cell undergoes a thorough mixing, either by a complete 
disintegration of cell wall, as well as cell content, or by a “ melting 
