39.—PHOTO-MICROGRAPH OF CULTURE OF _Bacillus bulgaricus_ IN MALT 126 40.—PHOTO-MICROGRAPH OF SMEAR FROM MILK THAT HAD BEEN ALLOWED TO SOUR SPONTANEOUSLY 126 41.—PHOTOGRAPH OF AGAR CULTURE, INOCULATED WITH A LACTIC POWDER 128 42.—PHOTOGRAPH OF TEST-TUBES OF STERILE MILK, INOCULATED WITH A TABLET PREPARATION SAID TO CONTAIN PURE CULTURES 128 43.—PHOTOGRAPH OF TEST-TUBES OF STERILE MILK, EACH TUBE HAVING BEEN INOCULATED WITH A TABLET OF A PREPARATION SAID TO CONTAIN PURE CULTURES 128 44.—PHOTOGRAPH OF TEST-TUBES OF STERILE MILK INOCULATED WITH A TABLET OF "LACTOBACILLINE" 130 45.—APPARATUS OF "LE FERMENT" CO. 129 46.—SOURED MILK APPARATUS OF THE MAYA BULGARE COMPANY, LIMITED 130 47.—LACTIC FERMENTS, LIMITED, APPARATUS 131 48.—MESSRS. ALLEN & HANBURY'S SOURED MILK APPARATUS 132 49.—VIRONELLE APPARATUS FOR SOURING MILK, MADE BY MESSRS. CLAY, PAGET & COMPANY, LIMITED 132 50.—"LACTOBATOR" MADE BY MESSRS. CHARLES HEARSON & CO., LIMITED 140 51.—MESSRS. HEARSON & COMPANY'S "LACTOBATOR" 142 52.—EDGAR'S "LACTOGENERATOR," SOLD BY THE DAIRY SUPPLY CO., LIMITED 143 53.—APPARATUS OF THE WILLOWS REFRIGERATING CO., LIMITED 144 54.—"LACTO" APPARATUS OF THE DAIRY OUTFIT CO., LIMITED 145 55.—STERILISING APPARATUS FOR STERILISING MILK ON THE LARGE SCALE 146 56.—ANOTHER METHOD OF STERILISING (DAIRY SUPPLY CO., LTD.). AN AMERICAN APPARATUS FOR PREPARING SOURED MILK 148 57.—AN AMERICAN APPARATUS FOR PREPARING SOURED MILK 149 THE BACILLUS OF LONG LIFE CHAPTER I INTRODUCTORY—HISTORICAL The milk industry is one of the oldest known to mankind, and it is difficult to imagine a time when milk in one way or another did not form a part of the diet of the human race. There is a good deal of evidence to show that in Paleolithic and Neolithic times, cattle were part of the possessions of the nomadic races; and, according to the Vedas, the manufacture of butter was known in India 1500 years B.C. In the eastern part of Europe, milk has always been looked upon as one of the principal kinds of food, but not necessarily the milk of cows, as, from ancient times to the present day, the milk from camels, buffaloes, sheep, and goats has been used indiscriminately throughout the East.