
70 STORRS AGRICULTURAL EXPERIMENT STATION. 
and moreover the differentiation of colonies is quite unsatisfac- 
tory upon agar plates. After trying various devices, we have 
finally adopted one that is in a measure successful. If we ex- 
amine our plates at the end of one or two days, the rapid lique- 
fiers are already evident and may be commonly detected at a 
glance. If they are numerous, the plate is hopeless; but if 
there is only a small number of them upon the plate, we fre- 
quently save it by dropping into the center of the colony a 
single drop of twenty per cent. sulphuric acid. When properly 
used, this stops the growth of the bacteria and checks the lique- 
faction. It is necessary to use a drop of the acid proportional 
to the size of the colony. If too much is added, the acid dif- 
fuses itself through the litmus and turns it red for some dis- 
tance around the colony, making it impossible to study the 
colonies of other bacteria within this particular area. If the 
drop is too small, it does not stop the liquefaction. If the drop 
is of the proper size, the acid does not diffuse itself through the 
gelatin, stops the liquefaction quickly, and does not injure the 
plate for further study. ‘The use of sulphuric acid in this way 
makes it possible to save for study many gelatin plates that 
would otherwise be totally ruined by the rapid liquefiers. This 
remedy for liquefaction is not possible if the rapid liquefiers 
are very numerous, but we have found, nevertheless, that it is 
extremely useful. In many cases it has made it possible to 
keep for many days, and to obtain satisfactory results from 
their study, plates which would otherwise be ruined by the . 
liquefiers before old enough for a satisfactory differentiation. 
Group VII. Slow liquefying type. These bacteria liquefy the 
gelatin very slowly, and frequently even after a week’s growth 
produce only small liquefying pits. Their presence in a plate, 
unless they are very numerous, does not interfere with the 
preservation and subsequent study of the colonies. They are 
commonly more abundant in fresh milk than is Group V., but 
are also later replaced by the acid bacteria. In the present 
paper we shall not attempt to differentiate this group into spe- 
cies, although it can be done easily. A considerable number 
of species are included in the group, most of which can be dis- 
tinguished easily by their colonies upon plates. All, of course, 
produce enzymes, and most of them are more or less putrefac- 
tive in their action. We believe they are of much significance 
