Bacteria in the Dainj.—In the ma jority of butter-making countries the cream is subjected to a process known as ripening or souring before it is churned; the cream is allowed to stand for from 12 to 17 hours, thus giving the bacteria an opportunity to grow in it. As a result the cream becomes some what soured, slightly curdled. Then the cream is churned. Not only does the ripened cream churn more rapidly and give a larger yield of butter than the sweet cream, but there are devel oped the peculiar flavor and aroma which are characteristic of the highest product. The dairymen in the great butter producing countries of northern Europe are making practical use of this knowledge and are utilizing pure cul tures of certain bacteria which have been found to be advantageous for the purpose of cream ripening and the production of agreeable flavors.
Nitrifying Bacteria.—Everywhere in fertile soil is a class of bacteria which has received the name of nitrifying bac teria. They feed on the soil ingredients and have the same effect on the simple nitrogen cleavage products the vinegar producing species have on alcohol—viz., bringing about a union with oxygen. Thus these nitrifying organisms form the last link in the chain that binds the animal kingdom to the vegetable king dom. For the nitrates are left in the soil, and may now be seized upon by the roots of plants and begin once more the journey around the food cycle. In
this way it will be seen that while plants, by building up compounds, form the connecting link between the soil and animal life, bacteria in the other half of the cycle, by reducing them again, give us the connecting link between animal life and the soil. The food cycle would be as incomplete without the agency of bacterial life as it would be without the agency of plant life.
Aids to Digestion.—The attention of investigators has been directed in modern times to a hitherto unknown class of bacteria which have a share in the proc ess of digestion in the stomach of man and the animals. It has long been known that the mouth, throat, intestines and other organs of the human system were inhabited by harmless bacteria. It was announced by Vignal that certain other microbes found habitually in the stomach possess properties similar to that of the saliva in aiding digestion. Numerous specimens were obtained and pure cultures made. With the artifi cially bred microbes a lot of experiments were tried. At least two kinds of organism were distinguished. One promoted the digestion of starch and an^:;,ier that of meat and albuminous substances. One acted most efficiently when it was slightly acidulated. The other needed to be a little alkaline. A third species seemed to have a special fitness for promoting the action of bile on fats.