146 PROCEEDINGS OF SECTION B. 
perly fed. The vinegar manufacturer has frequently to 
feed his bacteria, especially when he uses sugar instead of 
grain for his wort. 
Bacteria im the Dairy. 
’ Perhaps it would now be advisable to consider the dairy- 
ing industry in some of its bacteriological aspects. Mhik, it 
need scarcely be said, is a complete food, and when neutral, 
or nearly so, is a fluid exceedingly well adapted to grow 
bacteria. It is a common fallacy that the curdling of milk 
is always due to sourmg. It is just as often—and this 
applies to the milks obtainable in the neighbourhood of 
Sydney—caused by rennet enzymes secreted by bacteria, 
especially the sporeforming kinds. | Sydney milk is prac- 
tically unsterilisable. It can be sterilised by repeated and 
intermittent boiling, but this process alters the fluid, and 
it has then as much right to be called milk as butter heated 
in the same way can be called butter. The so-called sterile 
milks are such in name only, and contain bacterial spores, 
which are prevented from germinating by the absence of air. 
But should the smallest quantity of air obtain access, or, 
what comes to the same thing, should all the air not have 
been expelled in the steaming, the latent spores germinate, 
and the milk rapidly curdles. It will be noticed that in 
such cases the milk rarely has a sour taste. 
» . 4 
Pure “ Starters”? v. Manure Bacteria. 
In the souring of milk, the primary process in the manu- 
facture of butter and cheese, it is advisable to pasteurise_ 
the cream or milk by heating it for 15 to 20 minutes over 
68° C. ( = 154° F.)—the death-temperature of bacteria— 
and, after cooling, to infect with a “starter.” Starters are 
made by infecting a small quantity of pasteurised cream or 
milk with a pure culture of what should be a selected lactic 
bacterium. The “starter” has the same significance to the 
butter and cheese maker that the “sponge” has to the 
baker. Without previous pasteurisation the souring process 
cannot be so effectively done, on account of the secondary 
fermentations that ensue. I need not remind the reader 
that the chief source of the bacteria in milk is the manure 
that adheres to the udder of the cow, and so obtains access 
to the milking-pail. A small particle of manure contains 
myriads of bacteria of a most objectionable nature, and one 
small particle from each cow very soon becomes aggressive 
in the milk from a herd. It has been calculated that the 
