WATER. 



WEISSIA. 



time, and the sediment examined. Very 

 false results must also be obtained when 

 water is exposed to the air for any length 

 of time before examination, since Infusoria 

 and microscopic Algae always appear in a 

 short time, even in distilled water, when 

 exposed to the atmosphere; and an un- 

 covered water-butt or cistern will be found 

 a very fertile source of microscopic objects. 

 We regard the presence of most of those 

 organisms which do not sufficiently affect 

 the water to render its impurity discernible 

 by the naked eye, as a matter of little con- 

 sequence. Large numbers of Entomostraca, 

 certain Rotatoria and Infusoria, and Oscil- 

 latoriaceous Algae, generally very perceptibly 

 clouding or colouring the water, of course 

 indicate the presence of much decomposing 

 organic matter in the water, which, how- 

 ever, reveals itself very^ clearly in a short 

 time when the water is kept, by a fetid 

 odour. The presence of green Confervoid 

 Algae is by no means a sure sign of impurity 

 properly so called, in water ; for some will 

 only grow in very clear and pure water, 

 while many of them may be regarded as 

 agents of purification. The presence of 

 Zygnernaceae, Diatomacese, and especially 

 the Schizonaycetes, is, however, particularly 

 objectionable, as they become very fetid in 

 decomposition, which generally takes place 

 very soon when they are disturbed and 

 injured. When large numbers of minute 

 Algae appear in water, discolouring it over 

 extensive surfaces, the microscope will en- 

 able us to detect the nature of the object pro- 

 ducing the appearance, but will scarcely be 

 requisite to prove the impurity of the water. 



The microscope is also of great importance 

 in detecting the presence of undigested and 

 bile- stained particles of food, showing the 

 admixture of sewage with water. 



Coloration of water. Under this head 

 we shall refer to those plants and animals 

 which most commonly produce such ap- 

 pearances, premising that the commonest 

 cases of coloration depend upon suspended 

 mineral substances (mud), of different colours 

 according to the soils washed by the water. 



1. Producing a general green colour, or a 

 thick film on the surface. PROTOCOCCUS 

 ( Chlamidomonas, Ehr., Diselmis, Duj.), very 

 common in the spring ; and various Nosto- 

 chaceous Algae, as TRICHORMUS, OONIO- 

 PHYTUM, &c. (see NOSTOCHACE^E ; many 

 with a bluish tinge); CLATHBOCYSTIS (form- 

 ing a granular verdigris-green layer), Mi- 

 CBOHALOA, and various other PALMELLA- | 



CEJE and CONFERVACE^ EUGLENA viridis, 

 &c. The DESMIDIACE^E form greenish 

 patches at the bottom of water or on plants, 

 as do certain OSCILLATORIACE^E. 



2. Producing a red colour in fresh water. 

 ASTASIA hcematodes, Ehr. ; species of 

 DAPHNIA. TUBIFEX produces a red colour 

 on the mud in shallow water. Red forms of 

 species of PROTOCOCCUS (see also RED 

 SNOW). In salt water, DISELMIS Dunalii, 

 Duj.; TRICHODESMIUM. 



3. A brown cloudy appearance often ap- 

 pears in masses near the source of small 

 springs of water flowing out of blue clay, 

 or in pools on peat-bogs. This mostly con- 

 sists of peroxide of iron ; but sometimes a 

 similar brown appearance is produced in 

 pools by collections of amorphous granular 

 decaying organic matter, in which occur 

 great abundance of certain OSCILLATORS, 

 DIATOMACE^,!NFUSORIA, and ROTATORIA. 

 The obscure mycelioid structure called by 

 Kiitzing LEPTOTHRIX ochracea produces a 

 yellowish-brown tint ; DIDYMOHELIX also 

 gives abrown colour to water. Diatomaceae 

 often form a yellowish-brown coat on mud 

 at the bottom of water. Many Rotatoria 

 and the larger Infusoria (PARAMECIA, &c.), 

 when abundant give water a slightly milky 

 appearance. 



The ordinary method of separating the 

 organic bodies from water, is to place it in 

 a conical glass, and allow them to subside. 

 A little spirit or osmic acid should be pre- 

 viously added to prevent growth or repro- 

 duction. The bodies are then removed 

 with a pipette, or separated by filtration 

 through Swedish paper. 



The above list is undoubtedly very im- 

 perfect, but may afford some useful hints. 

 Microscopists who meet with such colora- 

 tions will naturally examine them carefully ; 

 they will find further information under the 

 heads of the articles cited. 



BIBL. Macdonald, Soc. Sci. Congress, 

 1877 ; Scott, Jn. Mic. Soc. 1877, Mn. M. 

 Jn. xviii. 237 ; Church, Water, 1877 ; Fox, 

 Food fyc. 1881; Cohn, Seitr. z. Biol i. 

 108; Blyth, Food $c. 1881; Frankland, 

 Water- Analysis. 



WATER-BEARS. See TARDIGRADA. 



WEBBI'NA, D'Orb. (Restricted.) A 

 subgenusof Trochammina ; adherent, single- 

 celled, moniliform, or alternating. Recent 

 and fossil. 



BIBL. Parker and Jones, Phil. Tr. civ. 

 435; P..J., & Brady, Monog. Crag For. 25. 



WEISSIA, Hedwig.-A genus of Pot- 



