┌─────────────────────┬───────────────┬──────────────┬───────────────┐ │ │TIME IN MINUTES│PRESENCE OR │PRESENCE OR │ │ │REQUIRED FOR │ABSENCE OF │ABSENCE OF MILK│ │ │FILTRATION OF 1│ULTRAMARINE IN│IN FILTRATE │ │ │PINT OF WATER. │FILTRATE. │ │ ├─────────────────────┼───────────────┼──────────────┼───────────────┤ │_Silicated carbon │ │ │ │ │ filter_ │ 68 │++ │+++ │ │_Carbon filter_ │ 18 │ + │+++ │ │_Maignen’s Filtre │ │ │ │ │ Rapide_ │ 4 │ 0 │ ++ │ │_Spongy iron filter_ │ 14 │ 0 │+++ │ │_Pasteur-Chamberland │ │ │ │ │ filter_ │420 │ 0 │ 0 │ │_Berkefeld filter_ │140 │ 0 │ 0 │ └─────────────────────┴───────────────┴──────────────┴───────────────┘ The number + indicates the relative amount of the experimental substances that made their way through the filtering medium. Experiments were then made with the actual microbes of certain infectious diseases, and it was found that certain filters allow these to pass. Thus a silicated carbon filter allowed 1,000 out of 15,000 typhoid bacilli suspended in water to pass through its substance; a manganous carbon filter allowed 600 to 800 out of 10,000 cholera vibrios to pass through; Maignen’s filter on the second day of experiment allowed 150 out of 5,000 cholera vibrios to pass through; Lipscombe’s charcoal filter experimentally only reduced typhoid bacilli from 20,000 to 5,000; the magnetic carbide filter only reduced them from 20,000 to 10,000; the spongy iron filter from 20,000 to 3,000; while, on the contrary, the Pasteur-Chamberland and the Berkefeld filter completely stopped all microbes and produced a sterile water. (As to these two, see page 98.) Of the materials enumerated =animal charcoal= was formerly regarded as an excellent filtering medium. It is capable of oxidising organic matter dissolved in water, but so far from sterilizing water, it favours the growth of microbes in it. Water filtered through charcoal, after the first few days of use of the charcoal, deteriorates, as the charcoal yields up impurities to it. =Manganous Carbon= consists of animal charcoal and black oxide of manganese mixed with oil, and heated strongly together out of contact with the air. The oxidising power of the carbon is said to be thus greatly increased. It shares the objections to carbon. =Silicated Carbon= consists of 75 per cent. of charcoal and 22 per cent. of silica, with a little oxide of iron and alumina. It is not an efficient filtering medium.