July, 1903.] 



KNOWLEDGE 



165 



cool and cold weather, be kept for a week or fortnight, and some 

 species, such as Meliirrta, occasionally for months if food- 

 material in the shape of fresh pond-water can be provided. 

 Failing pond-water, water from hay infusions, which mostly 

 contains quantities of bacteria and minute Infusoria, may be 

 added. The various species of Polyzoa and Sponges can also be 

 kept alive a considerable time by feeding them in a similar way, 

 but Hydras require a fare of Water-fleas if they are to thrive. 



For keeping microscopic life I have found no difference 

 between large and small aquaria, but the small tanks are the 

 more manageable; the great thing to be attended to is the 

 proper aeration with water plants, of which AnacharU, Fonte- 

 niil's, and T'(W.<»cWaare, perhaps, the best, and not to overstock 

 the tank with either animal or vegetable life. The water need 

 not be changed, but a little fresh j)ond water should be added 

 from time to time. Larger animals, such as small fish, water- 

 beetles and snails must be excluded altogether from small tanks, 

 and Polyzoa and Sponges must be kept therein in very 

 moderate quantity and small colonies only. 



In order to ensure success it is essential to maintain a proper 

 balance between the animal and vegetable life, and also to 

 supply fresh food frequently, for microscopical animals no more 

 than the larger beasts can live long without food. To some 

 extent, no doubt, they feed on each other, but in a small 

 aquarium their hunting ground is very limited and the game soon 

 becomes scarce. Asplanchnn can be seen under the microscope 

 to feed on Annraia, lirarhioniis, Pohjarthra, Triarihra, and 

 other Kotifers when it can catch them, and their shells and 

 remains are frequently found in Asplanchna's stomach. 



On the whole, the best plan is to go out and collect a fresh 

 supply from time to time and as often as may be convenient. 

 I may mention that at the middle of January, I had many 

 thousands of Rotifers in a tank which I collected two days 

 before in the Grand Junction Canal, near Westbourne Park 

 Station. The Canal was covered with blocks of ice, and the 

 time spent near the water did not exceed ten minutes, during 

 which I filled a large bottle with water condensed by means 

 of the ring net. 



Everyone who has worked at Pond-life will have experienced 

 how awkward it is to examine with a pocket lens and at 

 the same time attempt to pick out a particular animal in 

 order to place it under the microscope. In order to have both 

 hands free for this operation, and to keep the lens fixed to a 

 particular spot, I devised, some years ago, a small aquarium 

 microscope " ( Fig 2), which is simply a flat metal arm, jointed in 



Fro. 2.— Jlr. C. F. Rous^elcfs Tank Mirroscope and Window 

 Aquarium, with tlic Hat holtlc and collecting net. 



such a way that it allows the lens to be moved all over the sur- 

 face, but in one plane only, parallel to the side of the window 

 aquarium, whilst the lens is focusscd by a small rack and pinion 

 on the loft. The whole apparatus is screwed on to a small 

 wooden stand, on which the tank is placed. The lens used is 

 Zeiss' aplanatic combination x li diameters, which has wmking 

 distance enough to focus right through the tank, and sullicient 



• Made by C. Baker, of Higli Holborn, and described in Journal 

 Que/cel( Micro, Club, Vol. IV., 1890, pp. 53-5!.. 



amplification to enable one to recognise most Rotifers, Infusoria, 

 etc., and anything uncommon or new can at once be detected 

 and secured. Moving objects can readily be followed with the 

 lens, and pond weeds can be searched for anything that may be 

 growing on them, whilst the lens remains fixed in any position 

 it may be placed. I have had this tank microscope in constant 

 use for over twelve years, and can recommend it as thoroughly 

 practical, efficient, and time-saving. 



In a future paper I propose to describe those methods which 

 long experience has proved to be the most practical in the 

 examination of living objects under the microscope. 



The Qcekett MrcROSCOPic.vL Ct.fi}. — It may not be 

 generally known that, in connection with this Club, excursions 

 take place on Saturday afternoons during the summer season to 

 hunting grounds that invariably yield rich spoil to the 

 microscopist. Among the localities yet to be visited this 

 season are Wallington, Totteridge, Chingford, and Hadley 

 Wood. Those who may be interested in Pond-life and similar 

 subjects would derive many advantages from becoming 

 members of this Club, not the least of which is the opportunity 

 of joining these excursions. Communications should be 

 addressed to Mr. A. Earland, Reading Villa, Denmark Street, 

 Watford. 



AccuR.^TE WoRKixo. — The microscope never does its best 

 except the user apply his best abilities to its manipulation. It 

 is not to be expected that the worker who refers to his 

 microscope as a matter of necessity or routine can give to every 

 point the care that it deserves, and, indeed, properly requires, 

 but it is not too much to expect that these who are eng^ed in 

 original research, and those amateurs who have leisure and are 

 provided with everything that is the most perfect of its kind, 

 should employ it so as to secure the maximum effect. Those 

 who have seen the wonderful manner in which a Test Diatom or 

 a Rotifer will be displayed by one of our leading workers, will 

 be disposed to credit the objectives used with the greater part 

 of the effect, but it is almost invariably due to the exquisite 

 care which has been bestowed on the arrangements in every 

 small detail. So much of beauty and effect is lost through 

 want of care or lack of appreciation of essentials, that it behoves 

 those who use a microscope to devote to it all the practice and 

 thought that will enable them to wrest from it the best it is 

 capable of yielding. Enough has been written previouslj' of the 

 desirability of proportioning the aperture and power of the 

 substage conden.ser to that of the objective, and of its use and 

 adjustment, but it is scarcely recognised as it should be how 

 much the critical sharpness and definition can be improved by 

 the use of the mechanical draw-tube. 



Neither the complete aperture of the objective nor its fullest 

 correction for spherical aberration are utilised unless this 

 important consideration is studied, and this means, further, that 

 eyepieces of deep power cannot be so advantageously used if it 

 is neglected. Some workers are not possessed of a reallj' keen 

 critical eye, and are not readily able to decide whether an 

 objective works at its best within a variation of tube length of 

 three inches or more, but it is possible to so cultivate this 

 quality as to be sensible of a lessening of effect if the tube 

 length be varied so small an amount as one millimetre, that is, 

 assuming that every other detail has received equal attention. 

 It would be a good manipulative exercise for those who are 

 really interested in seeing all the microscope is capable of 

 revealing, to give careful attention to the minuter details, arnl 

 especially to the adjustment by tube length. 



Mounting Notes. — ihues innl Lirerwortg. — A correspon- 

 dent has sent some interesting suggestions arising out of the 

 article by Jlr. Russell on this subject. 



He remarks that '' Good glycorine-jelly will not deliquesce in 

 ordinary temperatures ; but, like all gelatinous substances, is 

 extremely sensitive to changes of temperature, more especially 

 when accompanied by moisture, expanding . and contracting 

 freely. The cement placed round the cover-glass is necessarily 

 rigid, and the cover-glass being usually finally cleaned while 

 hold between the thumb and finger, a little grease probably 

 adheres to an occasional edge. Presuming this to be so, wheu 

 expansion takes place tiny apertures permit the jelly to escape ; 

 in fact, when the cement extends some distance over the cover- 

 glass ca]iillarity actually invites such escape." 



