NEw YorK AGRICULTURAL EXPERIMENT STATION. 49 
sults of these investigations have appeared in a series of bulletins? 
of which this is a continuation. Before discussing the part taken 
by bacteria in the ripening process it seemed necessary to deter- 
mine as accurately as possible what kinds of bacteria are present in 
the cheese. This bulletin gives the results obtained from an in- 
tensive study of this phase of the problem during the past four 
years. 
The changes which take place in ripening cheese have been the 
object of many investigations. These changes are known to result 
from the combined action of a number of factors, of which bac- 
teria and enzyms are considered the most important. 
All attempts at determining the part taken by bacteria in the 
changes in cheese have been handicapped by a lack of accurate in- 
formation concerning the bacteria which are active during the rip- 
ening period. This lack of knowledge has not resulted from a fail- 
ure to appreciate the value of such information but rather from 
the difficulty of acquiring it. 
In the case of the cheese flora this difficulty is a very real one. 
The organisms which grow best in milk and its products do not 
flourish upon our artificial media and some forms do not grow 
there at all under ordinary conditions. Even when pure cultures 
have been obtained they are frequently lost before many observa- 
tions have been made upon them. 
ln morphology, many of these cultures are so near the horder 
line that a separation into the conventional coccus or bacillus is 
difficult; while their physiology is so variable that one wavers be- 
tween the extremes either of putting them all into a single species 
or of making as many species as there are cultures. The universal 
acceptance of species as the unit of biological classification at pres- 
ent requires its use here although the concept upon which it was 
founded can not be applied to bacteria. 
Species, as it was originally conceived and as it is at present used 
in the case of the higher plants and animals, is based primarily upon 
morphological similarity coupled with the ability to produce fertile 
offspring by sexual reproduction. In the case of bacteria the mor- 
phological basis for comparison or separation into species is slighr, 
and in the case of the cheese flora is reduced almost to the vanish- 
ing point; while sexual reproduction is entirely lacking in the 
whole bacterial group. ie 

a. ok. Aor. Exp, Sta; <Biles202;, (1007 ).;. 254, 215, 210, (1902)5 2313;.233, 
230,237, (1903); 245,<(1904).;) 261, (1905); Tech. Buls.\3, (1906)/; 4575, 
6, (1907). 
