. A treatise on hygiene and public health . to agrayish or colorless mass, in some cases looking almost like coarse belong to the class of cryptogamous (non-flowering) plants whichthe botanists call algai—plants which grow in the water, or in moistplaces, and usually contain chlorophyll {green coloring matter) or someallied substance. Plants of this character grow in almost all reservoirs,or other bodies of water exposed to the light and air, both in still andrunning water; they either float about in masses, or are attached more orless firmly to rocks and stones and other solid obj
. A treatise on hygiene and public health . to agrayish or colorless mass, in some cases looking almost like coarse belong to the class of cryptogamous (non-flowering) plants whichthe botanists call algai—plants which grow in the water, or in moistplaces, and usually contain chlorophyll {green coloring matter) or someallied substance. Plants of this character grow in almost all reservoirs,or other bodies of water exposed to the light and air, both in still andrunning water; they either float about in masses, or are attached more orless firmly to rocks and stones and other solid objects. By their growththey do no harm to the water in which they flourish ; and as they arereadily arrested by ordinary wire screens, or easily removed by rakes or 236 ON DRINKING-WATEE AND PUBLIC WATEE-SUPPLEES. scoop-nets, their presence causes no serious inconvenience in water usedfor town-supply. Fig. 2 shows several sorts of these algee as they appear when mag--nified: a is a spirogyra; b a zyg?iema ; and c an oedogonium ; the first. Fig. 8. two being shown in the process of conjugation. The different species oc-cur of a variety of sizes. These particular specimens are magnified be-tween 80 and 100 diameters. The vegetable organisms which cause the most trouble and inconvenience are those which appear as greenish specks, or minute straight orcurved threads, diffused through the water—visible enough if a large quan-tity of water be looked at, but perhaps almost escaping notice in thesmall quantity which would be taken up in a single glass. It is true thatthe individual plants are in some cases distinguishable by the naked eye;but their form and structure can be made out only by use of the micro-scope. If collected together as a scum, which often happens, especiallyon the windward shore of a pond, the scum is not coherent, is easilybroken up, either by a wind setting in the opposite direction, by a showerof rain, or by artificial agitation. The appearance has been sometim
Size: 1581px × 1581px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjecthygiene, bookyear1879
