. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . the water in the aspiration method, or may bedeposited in the tubes and bottles. These consider-ations, however, will only affect conclusions when ex-tremely refined work is desired. The Nature of the Suspended Matter. This is, of course, either animal or vegetable (dead orliving), or mineral. The more common substancesfound are :— Animal.— 1. Dead.—Debris from wear and tear of clothes, &c.;wool, silk, &c., fibres; human hair; p
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . the water in the aspiration method, or may bedeposited in the tubes and bottles. These consider-ations, however, will only affect conclusions when ex-tremely refined work is desired. The Nature of the Suspended Matter. This is, of course, either animal or vegetable (dead orliving), or mineral. The more common substancesfound are :— Animal.— 1. Dead.—Debris from wear and tear of clothes, &c.;wool, silk, &c., fibres; human hair; particles of feather;molecular debris (?) in considerable quantity ; debrisof dried epithelial cells, and epidermic scales fromskin ; pus cells; pyogenic micro-organisms ; frag-ments of insects, , scales from wings, legs, andparticles of the spiders web ; dried faecal particlesfrom horses dejecta, &c. 2. Living.—Minute ova ; infusorians—minute formseven grow in the atmosphere—chiefly amoebiform. Vegetable.— I. Dead.—Soot or particles of carbon, &c. ; moleculardebris (?) in large quantity; vegetable fibres, hairs, and PLATE A T^hte^-- iear Xcwa, pfJ?7^e^ Fupa ;:t Objects coramonly found in impure water (and air). SUSPENDED MATTER IN THE AIR. 229 cells, &c.; cotton, &c., fibres; starch grains; portionsof plants, and pieces of woody fibre ; pulverised straw ;dead spores, &c., of moulds, fungi, diatoms and bacteria. 2. Living.—Pollen seeds; spores of fungi, moulds,and diatoms (which may even live and grow in theatmosphere), and rarely mycelium of fungus ; algae,notably protococcus pluvialis, and also the small ovalcells of other unicellular algae ; bacteria and theirspores. Mineral.—Especially numerous when the ground isdry. Minute particles of every chemical constituent ofthe soil may be raised up into the atmosphere, , silica,silicate of aluminium, sand, mud, salts of sodium potas-sium and calcium (carbonate and phosphate), peroxideof iro
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