+-----------------+---------------------------------------+ | | Temperature. | | When Examined. +------------+-------------+------------+ | | 15° C. | 25° C. | 35° C. | +-----------------+------------+-------------+------------+ | After 3 hours | 10,000 | 18,000 | 30,000 | | After 6 hours | 25,000 | 172,000 | 12,000,000 | | After 9 hours | 46,000 | 1,000,000 | 35,280,000 | | After 24 hours | 5,700,000 | 577,500,000 | 50,000,000 | +-----------------+------------+-------------+------------+ Thus, after being kept in the laboratory for three hours the original 9,000 bacteria had in one case doubled, and in another more than trebled themselves. It will be seen that the temperature most favourable to the multiplication of these bacteria was 25 degrees Centigrade. If a sample of milk containing originally such a comparatively small number of bacteria--for a figure under 10,000 per cubic centimetre sinks into utter insignificance when we read of samples containing 2,500,000--if such relatively bacterially pure samples may support such prodigious numbers of these Lilliputians, what the microbial population of less satisfactory samples may amount to well-nigh baffles our powers of calculation. Professor Russell writes: "If we compare the bacterial flora of milk with that of sewage, a fluid that is popularly, and rightly, supposed to be teeming with germ life, it will almost always be observed that milk when it is consumed is richer in bacteria by far than the sewage of our large cities. Sedgwick, in his Report to the Massachusetts Board of Health for 1890, found that the sewage of the city of Lawrence contained at the lowest 100,000 germs, whilst the maximum number was less than 4,000,000 per cubic centimetre.[7] This range in numbers is much less than is usually found in the milk-supply of our large cities." [7] American sewage, it must be noted, is usually weaker and poorer in bacterial life than that of our country, by reason of the greater amount of water with which it is diluted. Numerous researches have been carried out during the last half-dozen years to try and localise the origin of some of the principal dairy troubles, with a view to their possible extinction, or at least control. In the course of these investigations quite a number of the bacteria found in milk have been successfully hunted down, and their offences brought home to them.