SCIENCE- GOSSIP. 



119 



•conducted by f. shillington scales, f.r.m.s. 



Flattening and Fixing Paraffin Sections 

 ■ON Slide. — In the " Journal of Applied Microscopy " 

 Mr. B. M. Davis recommends the alcohol method 

 for fixing paraffin sections on the slide in preference 

 to the water or albumin methods, as it entails less 

 risk of clouding in staining, and does not necessitate 

 the slides being absolutely clean. Mr. Davis tabu- 

 lates the essential steps as follows : («-) Flood the 

 slide with 70 to 85 per cent, of alcohol ; arrange 

 sections in order; hold slide a few inches above 

 small flame until sections are flattened, [h) Drain 

 off surplus alcohol (use filter-paper or cloth) ; re- 

 arrange sections in desired positions, (c) Cut out 

 two pieces of smooth blotting-paper same size as 

 slide. Wet one in same strength alcohol as used in 

 {a) and place over sections ; overthis put the other 

 piece dry ; pass small rubber roller (such as used 

 by photographer's) firmly over the dry blotting- 

 paper two or three times ; instead of using the 

 roller, any weight with smooth surface may be 

 pressed against the blotting-paper. The object of 

 this step is to flatten the sections completely, so 

 that. every part of the section will come in contact 

 with the slide, {d) Remove any lint which adheres 

 to the slide, and dry in a place protected from dust. 

 At the ordinary temperature of the room two or 

 three hours are necessary for complete drying. The 

 ■process may be hastened by keeping the sections at 

 a temperature a few degrees below the melting 

 point of the paraflin ; that is, below 40° C. If this 

 method has been carried out carefully, the sections 

 may be taken through as many stains or reagents as 

 desired, or left indefinitely in any solution which 

 will not act chemically on them. 



Fresh-water Aquaria. — The '• American 

 Naturalist " for March 1900 contained some notes 

 on fresh- water aquaria which may be useful to 

 those of our readers who take advantage of the 

 summer or autumn months to study pond-life, and 

 yet have never tried to keep their captures for 

 longer than . a few days, after which, without 

 further attention, th'e contents of the collecting- 

 bottle or receptacle become foul and useless. Mr. 

 L., Murbach, in the article alluded to, calls atten- 

 tion to the fact that most descriptions of fresh- 

 water aquaria insist oh the necessity for constant 

 change of water if the aquarium is to be per- 

 manent, whereas it is quite easy to so balance the 

 .animal against the plant life that the carbon 

 dioxide given out by the one is equalled by the 

 oxygen given forth by the other. The only thing 

 needing further attention is the feeding of such 

 animals as cannot themselves find their source of 

 food in the aquaria, and this must be clone so 

 carefully that no food is left to decay. It is also 

 essential that means be taken to prevent evapora- 

 tion and to exclude dust, etc. Suitable vessels 

 may be ireadily found, sucli as jam-jars, battery- 

 ;jars, and culture-dishes for the smaller window 



aquaria ; window-glass, properly cemented into 

 wooden frames that are kept coated with paraffin 

 or asphalt varnish, for a medium size ; and slate 

 bottom and ends, with plate-glass sides, for the 

 larger, though more expensive ones. In setting- 

 up the aquaria it is better to begin with water 

 from some clean pond containing considerable 

 plant and animal life. Fill up to within a few 

 inches of the top with water, and then add about 

 one twenty-fifth its bulk of plants and animals. 

 Rain or even hydrant water may be used, adding 

 some plants and later the animals desired. Where 

 there is no choice, snails and Crustacea are the 

 most convenient, unless they are hostile to the 

 organisms desired for experiment. The snails 

 feed on the plants, giving these carbonic acid 

 in turn for food, while the Crustacea feed 

 mostly on the debris from other organisms. If 

 the animals keep near the surface, too many are 

 probably present, and some must be removed or 

 more plants added. When the plants become 

 yellow they are too abundant or have not had light 

 enough. In some cases the water becomes foul on 

 first setting up the aquarium. As this is one way 

 of obtaining certain desirable results, keep it 

 covered until the foul odour disappears ; and if 

 new plants do not appear in time, add plants and 

 animals to suit, and it may prove to be the best 

 aquarium one has. Marine Protozoa have been 

 kept this way in jars brought from the sea-shore 

 several years ago. The pond scum (Algae) will be 

 strongl 3^ attracted by light to the sides of the glass, 

 so much so that by means of a tin stencil kept in 

 position when the light was strongest Mr. Murbach 

 was easily able to decorate the side of one of his 

 aquaria with his monogram in microscopic green 

 plants. Such aquaria as the foregoing might with 

 advantage be utilised in class- and school-rooms. 

 In one jar were kept Amoebae and other Protozoa, 

 whilst another contained in addition diatoms, 

 Oscillaria, some water-fleas, and Rotatoria. An- 

 other larger one, kept two and a half years, in which 

 a large snail, some water weed, and smaller animals 

 constituted the balance, furnished sun-animalcules 

 for demonstration. The largest one had been kept 

 nearly two years without change or addition of 

 water. It was stocked with aquatic plants : Clado- 

 p?iora, Myriophylluvi, Leinna^ Woljfia, AnacJiaris, 

 and many single-celled algae. The largest animal 

 representative was a so-called " bull-head," one of 

 the species of Uranidae, about four inches long, 

 kept principally for the balance, and because he 

 needed no further attention than a few earth- 

 worms every few days. In this aquarium fresh- 

 water polyps, Polyzoa, and other interesting forms 

 appeared in their season. Mr. Henry Scherren, in 

 his "Ponds and Rock Pools,"recommeiicls a northerly 

 aspect, for choice, and that direct lateral illumina- 

 tion should be avoided, and mentions specifically as 

 suitable plants the Italian water-weed {ValliHneria 

 spiralis) in a small pot, which can be bedded in 

 the gravel about the centre of the tank ; frog-bit 

 {Hydrooharis viorsus-ranae) ; the Canadian water- 

 weed (JnacJiaris alsinastriini), which gro¥/s only 

 too rapidly; the common spiked milfoil {Myrio- 

 plnjllum spicatmn), a spray of which, fairly rich in 

 animal life, can be dropped into the aquarium, 

 and affords a home for tube-building Rotifers ; 

 also hornwort (CeratopJiyllmn. devierswm), the water- 

 crowfoot (^Raomnculus aquatilis),- the water star- 

 worts (CallUricJtevernacind Cautmimalis), a spray 

 or two of bladder- wort ( Utrlcidariavulyaris'), willow 



