MICRO-ORGANISMS. 147 
people of Berlin consume half a ton of manure in their milk 
per diem. This can easily be imagined when one remembers 
the rhyme of one’s childhood—“ A little drop of water, a little 
grain of sand, &c.’’ It is, therefore, evident that pasteuri- 
sation of milk in the dairy, the factory, and the home is 
advisable on hygienic and practical grounds. But to return 
to the starter. This should be prepared originally from an 
indigenous species, which was done by the authors of a 
paper read before this Association two years ago. To show 
the necessify for selecting the races, it has been shown that 
from one sample of milk, races of the same bacterium have 
been separated, some of ‘which produced twice the amount 
of acid that others did. The imported pure cultures of 
lactic bacteria are preserved in some such material as starch, 
which appears to be a source of impurity, because, when the 
bottles are opened in this country, they are found to contain 
cultures of the common moulds, and generally no lactic bac- 
teria. 
The Aroma of Butter. 
«: . 
Bacteria are also useful in imparting to butter an agree 
able and pleasant aroma. _ Perhaps the best-known of the 
aroma bacteria is Bacillus Connu (or Conn 41), which un- 
doubtedly improves the quality of butter prepared with its 
aid. I have tested this bacterium experimentally, and the 
difference between butters made from one lot of cream with 
and without it was very marked. 
, 
Commercial Pure Cultures. 
Commercial pure cultures consist of some absorbent sterile 
powder, such ag starch or sugar, impregnated with a pure 
culture of the bacterium. The pure culture is grown upon 
suitable solid media, and scraped off, distributed in water, 
and mixed with the absorbent powder, dried, and sealed up ; 
or a fluid culture is scattered over the powder, which is 
subsequently dried at a low temperature. Theoretically, 
there is no difficulty in the process, but practically the 
utmost care is needed to conduct these simple operations in 
an aseptic manner, so that the finished dry powder contains 
the’ required living bacteria, and no other micro-organism. 
The Rincning of Cheese. 
In the making of cheese the lactic bacteria are all-im- 
portant in acidifying the milk for the production of a good 
rennet curd. To convert the tasteless curd into a mellow 
cheese some agent is needed. We know that in some kinds 
