i86 



SCIENCE- GOSSIP. 



MICR05C0PYI 



conducted bt f. shillington scales, f.r.m.s. 



Colouring of Water by Micro-Obganisms. 

 Much curiosity and speculation have been aroused 

 in the neighbourliood of Stoke Bridge, Ipswich, by 

 the turbidity and deep chocolate colour of the 

 river Orwell, reaching for some little distance from 

 each side of the bridge. This appearance has been 

 ascribed by some to the scourings of the maltings, 

 by others to spawn, also to the sun, or to the 

 remains of star and jelly fish. This remarkable 

 coloration of the river is in streaks of a greater 

 or less width, and extends but a few inches beneath 

 the surface, whilst on the decline of the sun the 

 colour wholly disappears. This phenomenon is 

 caused by countless myriads of beautifully marked 

 plants of a deep chocolate shade. This colouring 

 matter can readily be discharged by chemical 

 reagents and the green structure of the plant 

 rendered apparent, or by the action of iodine the 

 presence of starch can readily be determined. 

 These plants bear a striking similarity in their 

 movements and power of contractility to the fresh- 

 water Euglena, but in form they resemble a 

 bicuspid tooth, with a deep cleft on each side of the 

 axis. The two fangs might be taken to represent 

 the head, and the crown the base ; each plant being 

 about the gnggth of an inch in diameter. Some 

 hundreds of these org:amsms may be seen gaily 

 disporting themselves in a drop of water scarcely 

 exceeding in size a pin's head, the whole being in 

 a rapid .state of motion. These brackish water 

 organisms are delicate, breaking up a few hours 

 after being removed from their habitat. The plants 

 appear to come up with the tide, and are not due 

 to the presence of sewage or other preventable 

 matter. — Alfred Martmelli, Ipsniieli. 



[See an article on the " Colouring of Water by 

 Micro-organisms," by Mr. James Burton, which 

 appeared in SciENCE-GossiP, vol. vii., pp. 332. 

 333. — Ed. Microscopy, S.-G.] 



Peepaeing Crystals for the Microscope. — 

 The "American Monthly Microscopical Journal" 

 reprints an article by Mr. (3. E. Dowdy that origin- 

 ally appeared in the " Pharmaceutical Journal." 

 The article deals with the preparation of crystals 

 as microscopic objects, and we summarise it 

 as follows. The slides and cover-glasses must be 

 carefully cleaned before starting work, so as to 

 ensure their freedom for use. This maybe secured 

 by washing them with ammonia or other solvents, 

 rinsing with distilled water, drying with a clean 

 rag, and finally polishing with chamois leather. 

 One of three metliods can then be adopted for 

 preparing the slide. The first consists of evapo- 

 rating down a saturated solution of the salt until 

 enough moisture has been driven off to enable the 

 crystals to rapidly form on cooling. Make a satu- 

 rated solution of the salt in distilled water, and 

 with a pipette deposit a drop in the centre of the 

 slide ; slope the slide to make the liquid spread in 



a film, and absorb the superfluous moisture from 

 the side of the slip with blotting-paper. Then 

 hold the slide, with the wet side uppermost, over 

 the flame of a Bunsen or spirit lamp at such a 

 distance that the liquid just steams. Continue 

 this until a thin film of the salt forms at the 

 edges ; then withdraw ; allow to cool, and examine 

 under the microscope. If satisfactory, mount 

 permanently by depositing a drop of cold xylol 

 balsam over the film, and covering with a clean 

 cover-glass. If the salt be insoluble in water, a 

 .suitable solvent, such as alcohol, chloroform, &c., 

 may be employed ; in which case rapid evapioration 

 will, of course, take place without the aid of heat. 

 These crystals will probably require a different 

 mounting medium, such as castor-oil, or one in 

 which they are not soluble. Dr. Lankester re- 

 commends dissolving a little gelatin or gum acacia 

 in distilled water, and adding to this a few drops 

 of a saturated aqueous solution of the salt. A 

 drop of the warm mixture is then deposited on a 

 slip, superfluous moisture drained oft', and the slide 

 allowed to cool. With some salts — i.e. copper 

 sulphate, iron sulphate, &c. — remarkably beautiful 

 crystalline forms make their appearance, often in 

 flower- or fern-like patterns, the forms varying 

 according to the temperature, and consequently 

 upon the loss of varying proportions of water of 

 crystallisation. Epsom salts, potassium chlorate, 

 potassium bichromate, or in fact any salt soluble 

 in water, will lend itself to the above process. 



The second principal method is by fusion, a more 

 restricted, but not less effective method than the 

 foregoing. Though equally simple, the process is 

 not, however, as uniformly successful. Salicine is 

 a good substance with which to experiment. Place 

 a small quantity on the centre of a thin slip and 

 heat over a flame until it just fuses ; withdraw from 

 the heat before it chars, and allow to cool gradually. 

 If successful, small circular plates or rosettes will 

 appear on the film, wdiich may then be mounted as 

 usual in cold xylol balsam. Good slides of this 

 description make beautiful objects for dark-ground 

 illuminations or for polarised light. This method 

 is useful in enabling one to prepare totally different 

 physical forms from the same salt. AVith salicine, 

 for instance, an aqueous solution deposits needle- 

 shaped crystals, quite distinct from the circular 

 form obtained by fusion. Too much salt on the 

 slip must be avoided, as on cooling the film would 

 thus have a tendency to star and crack. If the film 

 should be too thick to be viewed as a transparent 

 object, it will often make a good opaque object by 

 pasting a circle of black paper on the under side of 

 the .slide. Crystals of fatty substances — spermaceti, 

 hard paraffin, etc. — are prepared in a similar way. 

 It is only necessary to place a small piece on 

 a slide, warm it, and when melted press a cover- 

 glass on it ; the crystals form as the mass cools. 

 Such crystals have an added interest in that by 

 simply warming the slide before viewing it the 

 actual formation of the crystals can be watched 

 under the microscope any number of times. The 

 third principal method is still more limited in 

 application, being confined to those substances 

 which are easily volatilised, and crystallise on 

 cooling. Preparation of slides by sublimation is 

 as follows. A suitable chemical — benzoic acid, for 

 instance-is placed in a dry narrow test-tube, and 

 the latter is then held over the flame until the acid 

 volatilises, the tube being then inverted and stood 

 on a cold slide. The characteristic crystals will 



