Page:Popular Science Monthly Volume 35.djvu/227

Rh fermentation of milk is traced to the growth of a microorganism known as Bacterium lactis, which converts the milk-sugar into lactic acid. The work of decomposition is then taken up by another bacillus, named subtilis, through which butyric acid is produced. Recent experiments made in the cultivation of milk bacteria by Baginski indicate that the Bacterium lactis is incorrectly named, and, being responsible for an acetic-acid formation, is better termed aceti.

There is also a peculiar fermentator, Bacterium coli, that refuses to meddle with milk-sugar alone, but upon the addition of white of egg shows extraordinary activity, furnishing lactic, formic, and acetic acid. These three—Bacterium aceti, Bacillus subtillis, and Bacterium coli—are the normal visitants of milk, and the changes dependent upon their presence are well understood. The microorganisms that breed disease and death appear under exceptional circumstances, against which, so far as they are known, we may carefully guard.

The bacilli of phthisis, typhoid, and scarlet fever have been detected in milk supposed to be wholesome. Thorough inspection of cattle and dairies may reduce the frequency of infection; but, until such supervision is the rule, all danger can be avoided by boiling the milk. In the late Congress at Paris on the study of tuberculosis. Dr. Nocard advised this to be done in every case where there existed any tendency to consumption.

A peculiar sickness, which in its malignant form is similar to anthrax, has been traced to a germ occurring in milk. The conditions required for its development are known, and have been artificially produced by feeding cattle with fodder exposed to the dew-fall. The poison is found in sweet milk, butter, cream, and cheese, but not in buttermilk. It is either formed in small quantity, or has the property attributed to it of self-attraction. Neither the ptomaine nor the bacillus producing it has been determined, and they offer a new field for experiment.

The chief mischief-maker is yet unknown, unless it may possibly be identical with the micrococcus found by Dr. Sternberg in cheese. Its ptomaine, however, was isolated by Prof. Vaughan, of the University of Michigan, in 1885, and was called, from the substance in which it was discovered, tyrotoxicon—cheese-poison.

The history of this discovery is interesting. Three hundred cases of cheese-poisoning were recorded in Michigan by the Board