198 BACTERIA IN BUTTER AND OLEOMARGARINE 
bers of all species of bacteria than were found at first. During this 
time, however, the lactic acid bacteria, especially of the Bact. 
lactis acidi type, increase more rapidly than the others. In the 
very fresh cream this species may have been comparatively small 
in numbers, forming not more than x or 2 per cent. of the whole, 
but the percentage rises rapidly. After several hours, the time 
varying with different specimens, the acid bacteria constitute a 
large proportion of the whole. From this time, after they form 
perhaps 50 per cent. of all the bacteria present, the other species 
begin to be seriously affected by the acid produced. ‘The acid- 
forming germs still continue to increase in numbers, while the 
others cease to grow so rapidly, soon begin to diminish, and 
finally may largely or wholly disappear. The result of this is that, 
during the last stages of the ripening, there may be present in the 
cream nothing but acid bacteria, which sour the cream and pro- 
duce the final changes in the ripening. 
Thus it will be seen that the ripening of cream may be divided 
into two stages. In the first the growth of the miscellaneous 
species of bacteria continues, and all types may become more or 
less abundant. In the second the acid-forming germs gradually 
force the others into the background and finally crowd them out 
entirely. Both of these stages doubtless contribute to the final 
product. Without the proper lactic organisms it is impossible to 
get the proper flavored butter. But butter made from pasteurized 
cream and ripened by pure cultures of lactic acid bacteria does not 
develop so much flavor as that in which the original bacteria are 
allowed to grow with the acid germs. Hence, it is probable that 
the development of the miscellaneous bacteria in the first phase of 
the ripening has not a little to do with the final butter flavors. 
The Effect of Different Species of Bacteria.—The butter- 
maker thus needs bacteria, but he must have the right kind. 
When cream_jis collected for a large creamery from many sources 
there are sure to be in it quantities of different varieties of bacteria, 
each patron contributing his quota. Each species may be ex- 
