858 The American Naturalist. [October, 
has exerted upon argricultural pursuits without stating the 
position of it with reference to dairying. ; 
Milk, like every other organic substance, is subject to certain 
changes, and these conditions are now known to be directly 
traceable to the influence of micro-organisms. These so-called 
“ diseases" of milk are mainly fermentative in their character 
and modern bacteriology has shown the dairyman that they 
can be entirely prevented if he handles his product in a 
rational way. Milk, as it comes from the cow, is entirely 
devoid of germ life, but its high degree of temperature when 
freshly drawn and the exceedingly nutritious food medium 
that is offered, afford the optimum of conditions for the devel- 
opment of any bacteria that find their way into the fluid. The 
ubiquity of distribution of fermentative organisms render it 
impossible to entirely avoid their action, but the losses of the 
milk-dealer can be greatly diminished if cleanliness is scrupu- 
lously observed. 
While the milkman wishes to avoid bacteria as far as possi- 
ble, the buttermaker should welcome them as his friend. 
Many forms are, of course, undesirable, but from the recent 
investigations in this field there is no question but that the 
bacterial content of butter largely influences its keeping qual- 
ities as well as the peculiar flavor for which such fancy prices 
are paid. The process of “ ripening” or “ souring " cream that 
is practiced by every butter maker is a natural bacterial fer- 
mentation. Better and more butter is obtained from ripened 
than from “sweet” cream. If this is so, the question naturally 
arises, Why can we not isolate the forms that are capable of pro- 
rucing these changes and add them directly to the cream rather 
than to trust to their sponta development? The researches 
of Hansen in the realm of pure yeast ferments have revolution- 
ized the brewing industry within the last five years, and the 
introduction of pure cultures of yeast for fermentative purposes 
has made a better, and what is still more important, a [more 
uniform product. Now the same field seems to be opening in 
the process of butter-making. Danish and German creameries 
are now being supplied with pure bacterial cultures that are 
