WATER. 



[ 816 ] 



WEISSIA. 



time, and the sediment examined. Very 

 false results must also be obtained when 

 water is exposed to tlie air for any length 

 of time before examination, since Infusoria 

 and microscopic Algte always appear in a 

 short time, even in distilled water, when 

 exposed to the atmosphere; and an un- 

 covered water-butt or cistern wiU be foimd 

 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 niunbers of Entomostraca, 

 certain Ilotatoria and Infusoria, and Oscil- 

 latoriaceous Alga3, 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 

 odoiu'. The presence of green Confervoid 

 Algfe is by no means a sure sign of impurity 

 properly so called, in water ; for some will 

 only grow in -sery clear and piu'e water, 

 while many of tliem may be regarded as 

 agents of purification. The presence of 

 Zygnemacese, Diatomacese, and especially 

 the Schizomycetes, is, however, particularly 

 objectionable, as they become very fetid in 

 decomposition, which generally takes place 

 very soon when they are distm-bed and 

 injured. When large numbers of minute 

 Algae appear in water, discolouring it over 

 extensive sm-faces, the microscope wiU 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 mici'oscope 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 iVfiter. — • 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 tlitterentcolours 

 according to the soils wa^^hed by the water. 



1. Producing a general f/recn colour, or a 

 thick film on the surface. — Protococcus 

 ( C/damidonionas, Ehr., Diselmis, Duj. ), very 

 common in the spring ; and various Nosto- 

 chaceous Algfe, as Tiuchoemus, (.'oxio- 

 PHYTUM, &c. (see NosTocHACKiK ; many 

 with a bluish tinge); Cj.atiirocv.stis (form- 

 ing a granular verdigi'is-green layer), Mi- 

 ciiOHALOA, and various other Palmella- 



CE^ and CoxFERVACE^ ; Euglena viridis, 

 See. The Desmidiace^e form greenish 

 patches at the bottom of water or on plants, 

 as do certain Oscellatoriace^b. 



2. Producing a 7-ed colour in fresh water. 

 — Astasia hmnatodes, Ehr. ; species of 

 D.\piES'iA. 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 ii'on ; but sometimes a 

 similar brown appearance is produced in 

 pools by collections of amorphous granular 

 decaying organic matter, in which occm* 

 great abundance of certain Oscillatorle, 

 l)iATOMACE^,IxFrsoRiA, and Rotatoria. 

 The obscure mycelioid sti'uctm'e called by 

 Kiitziug Leptothrix ochracea produces a 

 yellowish-brown tiut ; Didymohelix also 

 gives abrown colour to water. Diatomaceae 

 often form a yeUowdsh-browu 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 httle spirit or osmic acid shoidd be pre- 

 viously added fo prevent growth or repro- 

 duction. The bodies are then removed 

 with a pipette, or separated by filtration 

 thi'ough hwedish paper. 



The above list is undoubtedly very im- 

 perfect, but may afford some usefid hints. 

 Microscopists who meet with such colora- 

 tions will naturally examine them carefully; 

 tliey will find f lu tlier 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 4''C. 1881; Cohu, Beit)-, z. Biol, i, 

 108; Blyth, Food ^r. 1881; Frankland, 

 Water- Analysis. 



WATER-B1:aRS. see Tarbigrada. 



WEIJBI'NA, D'Orb; (Restricted.)— A 

 anhgewnSioi'J'rochainminu ; adherent, single- 

 celled, mouiliform, or alternating. Recent 

 and fossil. 



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

 4-35; P.,J., & Brady, ilfa?K)(/. Crag For. 25. 



WEISSIA, Iledwig.— A genus of Pot. 



