May 1905 ] Suggestions from the Study o f Dairy Fungi 
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2. Gelatine. 
The diagnostic value of the liquefaction of gelatine is ques¬ 
tioned by some, but within certain limits I believe it to be very 
useful. Colonies of some species never produce such liquefac¬ 
tion, other colonies will be floating entirely free in a pool of 
liquid within a week (ex. Cladosporium herbarum) and always 
produces such an effect. The character is very reliable as an 
accessory to other data; in such cases many species produce slight 
liquefaction, some liquefy the gelatine under the center of the 
colony, remaining always with at least a sterile vegetative bor¬ 
der of mycelium in the solid substratum, some produce a semi¬ 
liquid condition in the whole plate but no watery fluid. In these 
latter cases especially this is difficult to describe accurately and 
perhaps unreliable because the extent of change is often both 
variable and dependent upon conditions which cannot be accu¬ 
rately determined. However, this indefinite condition should be 
described and recorded as carefully as observations will permit. 
Whether the liquefaction of gelatine is to be regarded as an 
index of enzyme production will be discussed in another paper, 
but the question is entirely too indefinitely understood to give it 
a diagnostic value as great as some bacteriologists assume it to 
have. Further, it must be noted here that the same species gives 
different reactions to gelatine media of different formulae so that 
much care is necessary in stating results of this kind. 
3. Indicators. 
The introduction of a sterile solution of litmus or other indi¬ 
cator gives many interesting contrasts. With litmus in media 
acidified by two to five drops of normal lactic acid, cultures of 
some species uniformly show a prompt and sharp change from 
red to blue, beginning as soon as the growth becomes visible 
to the eye. Cultures of other species show no change for sev¬ 
eral days, the time here being fairly characteristic, then with the 
change of color in the fruiting portion of the mycelium (or about 
that time) the medium begins to turn blue below the center of 
the colony and this color progresses outward until usually the 
entire plate or tube of medium has become blue. In still other 
species a red medium remains red during its entire growing, and 
fruiting period. If the medium be neutral or alkaline those which 
turn red to blue will leave the blue entirely unchanged, others 
will change the blue to red for a time varying with the species 
after which it progressively changes back to blue, beginning at 
the center as before; others will turn the blue to red and it will 
remain so. Similarly here we find every gradation in rate and 
intensity of action which brings into notice some species whose 
effect is neutral, giving the shades of color characteristic of the 
turning point of litmus and other soecies in which discordant 
results are obtained from causes not yet determinable. Such 
