126 Report oF DEPARTMENT OF BACTERIOLOGY OF THE 
failure of the gas to appear in the tube is due to its-solution 
in the liquid media and partial diffusion through the open arm 
of the tube. The ability of the liquid to hold appreciable 
amount of gas in solution is illustrated by the bubbles of gas 
which appear in the top of the tube after the medium has 
been heated in the sterilizing process and again disappear on 
cooling. i 
While exact measurements are lacking it is probable that 
the gas of respiration does not nearly saturate the fluid in 
the fermentation tube so that the appearance of gas in 
the closed arm does not mark the beginning of the true fer- 
mentative action but rather a somewhat advanced stage of this 
action. Conversely, when dealing with a group of cultures 
which are on the turning point of the formation of visible 
gas, the failure of the gas to appear does not necessarily mean 
that the ability to ferment the sugar in question has been lost 
but rather that it has been so diminished as not to super- 
saturate the fluid in the tube. The fact of the continuation 
of the growth in the closed arm and of the formation of acid 
in these fermentation tube cultures lends color to the idea 
that the sugar is still being attacked in the same general way 
though less vigorously than before. 
CLASSIFICATION. 
Classification in a case like this may serve either of two 
distinct ends. It may assist future students to recognize the 
relationships of cultures which they may study dnd it may be 
of service to the farmer in showing whether the form which 
is present on a given crop will be dangerous to a succeeding 
crop which he may desire to grow later on the same soil. 
Because of the limited knowledge of germ life which is now 
available, any classification of such forms must be considered 
as tentative and as merely expressing the judgment of the 
authors concerning the relationships under discussion. In 
this connection it should be stated that some of the doubtful 
points in this classification were referred to six of our friends 
whose judgment was considered as of especial value in such 
matters. There was such a wide variation in what they con- 
