[4] Migula has recently (1896) suggested that the Schizomycetes should be subdivided into Coccaceæ, Bacteriaceæ, Spirillaceæ (spirilla, spirochæta), Chlamydobacteriaceæ (Streptothrix, Crenothrix, Cladothrix), and Beggiatoa.
[5] A one-twelfth oil immersion lens is requisite for the study of the lower bacteria.
[6] A flagellum is a hair-like process arising from the poles or sides of the bacillus. It must not be confused with a filament, which is a thread-like growth of the bacillus itself.
[7] A "pure culture" is a growth in an artificial medium outside the body of one species of micro-organism only.
[8] Some pathogenic germs (suppuration and typhoid) can withstand freezing for weeks.
[9] G. J. Romanes, Darwin and After Darwin, vol. ii., 231.
[10] It will be observed that there is a marked difference between the effects of dry heat and moist heat. Moist heat is able to kill organisms much more readily than dry, owing to its penetrating effect on the capsule of the bacillus. Dry heat at 140° C. (284° F.), maintained for three hours, is necessary to kill the resistant spores of Bacillus anthracis and B. subtilis, but moist heat at fifty degrees less will have the same effect. It is from data such as these that in laboratories and in disinfecting apparatus moist heat is invariably preferred to dry heat. For with the latter such high temperatures would be required that they would damage the articles being disinfected. Koch states the following figures for general guidance: Dry heat at a temperature of 120° C. (248° F.) will destroy spores of mould fungi, micrococci, and bacilli in the absence of their spores; for the spores of bacilli 140° C. (284° F.), maintained for three hours, is necessary; moist heat at 100° C. (212° F.) for fifteen minutes will kill bacilli and their spores.
[11] Water from a house cistern is rarely a fair sample. It should be taken from the main. If taken from a stream or still water, the collecting bottle should be held about a foot below the surface before the stopper is removed.
[12] The cubic centimetre (cc.) is a convenient standard of fluid measurement constantly recurring in bacteriology. It is equal to 16–20 drops, and 28 cc. equal one fluid ounce.
[13] The gelatine is reduced to liquid form by heating in a water-bath. Before inserting the suspected water it is essential that the gelatine be under 40° C, or thereabouts, in order not to approach the thermal death-point of any bacteria.