SCIENCE-GOSSIP. 



185 



CONDUCTED BY J. H. COOKE, F.L.S., F.G.S. 



To whom Notes, Articles and material relating to Microscopy, 

 and intended for Science-Gossip, are, in the first instance, 

 to be sent, addressed "/• H. Cooke, Edlestone, Battenhall 

 Road, Worcester." 



To Microscopists. — When engaged on micro- 

 scopical manipulations the needs of the situation 

 often necessitate the making of simple home-made 

 apparatus and the use of practical expedients. 

 Being of so simple a nature it does not often occur 

 to the microscopist that a knowledge of his 

 methods might be of use to fellow-workers, and 

 thus many valuable hints and methods are lost 

 to all but himself. We would remind our readers 

 that our columns are always open to such sugges- 

 tions, queries and hints, and that, whenever 

 practicable, reproductions will be made of suitable 

 sketches. 



Alcohol as a Hardening Reagent. — As a 

 general hardening fluid there is perhaps none 

 which is so universally applicable as alcohol. 

 Small pieces of tissue not exceeding one-eighth to 

 one-quarter of an inch in diameter should be placed 

 in ninety-five per cent, alcohol. The volume of 

 alcohol used ought to be about twenty times as 

 great as the tissue to be hardened. If less is used 

 it should be renewed at the end of a few hours. It 

 is also advisable to place a small quantity of 

 absorbent cotton in the dish or bottle containing 

 the hardening fluid. The alcohol used for hardening 

 the tissues should be renewed every day for the 

 first three days, and if the pieces are not large, 

 they will be well hardened in four or five days, and 

 may be prepared for further manipulation. Or, if 

 this be not possible, they should be transferred to 

 eighty per cent, alcohol, in which they may be 

 stored away for future use. 



Demonstrating Blood Circulation. — Mr. T. 

 O. Mabry, of the University of Mississippi, contri- 

 butes to the " Journal of Applied Microscopy," an 

 interesting note on a simple and convenient method 

 for demonstrating the circulation of the blood in 

 the capillaries of the external gills and in the 

 transparent tissues of the tail of the tadpole. 

 Tadpoles are to be preferred to frogs for this 

 purpose, because they are more easily obtained 

 and their tissues are thinner and more transparent. 

 In them one can see the branching of the arterioles 

 remarkably well ; and the systole and diastole of 

 the heart are plainly noticeable in the alternating 

 increase and decrease in the rate and flow of blood 

 in the capillaries. The principal difficulty met 

 with in the use of tadpoles is their liveliness. 

 This Mr. Mabry overcomes in the following 

 manner : a moist tadpole was placed in a thin 

 transparent sheet of collodion, without pinning and 

 without using a cover-glass. The experiment was 

 a success. The water softened the collodion and 

 made it sticky, so that the tadpole's tail became 

 glued fast. Mount moist, not using too much 

 water, and examine with a two-thirds inch 

 objective. 



Tongue of Blowfly.— When the head of a 

 blowfly is severed from the body the tongue is apt 

 to collapse. A slight pressure on the head will 

 expand it. A beautiful specimen of the expanded 

 tongue may be secured by splitting a small stick 

 for a short distance, and, before removing the 

 knife-blade, placing the head between the separated 

 parts. When the blade is withdrawn, the head 

 will be compressed and the tongue expanded. 

 Immerse stick and tongue in turpentine and leave 

 for a few days, after which it will be found well 

 cleaned and cleared, and can immediately be 

 mounted in balsam. 



Pond Life on Gelatine Plates. — While 

 examining some ordinary photographic plates 

 under the microscope, Mr. W. G. Levison found 

 an interesting way of catching and holding minute 

 organisms for examination under the microscope. 

 He found numbers of these forms adhering to 

 gelatine - coated photographic plates after the 

 plates had been in the water the usual time 

 allowed for washing them, after coming out of the 

 hypo solution. The number of forms varied with 

 the length of time the plates were in the water. 

 By placing the plates in a box used for washing 

 the hypo from the plates and allowing the tap 

 water to run through it, he collected on them a 

 few large diatoms, many smaller ones, and a large 

 number of small active ones. When the film had 

 become soft, after being in the water several days, 

 Vorticellae and other Infusoria appeared, anchored 

 to the film. His experiments led him to believe 

 that these plates can be successfully used to collect 

 pond life by leaving them a greater or less time 

 submerged in the pond. 



Air Bubbles and Oil-Globules.- — It is of 

 importance to be able to identify and distinguish 

 between air-bubbles and oil-globules in preparations 

 under microscopical investigation. The appearances 

 of both vary considerably according to the portion 

 of them that happen to be in focus. Dallinger, in 

 " The Microscope and its Revelations," represents 

 and describes these different aspects, as presented 

 when light is transmitted from a concave mirror 

 exactly centred and a diaphragm of about two- 

 thirds of a millimetre is placed at a distance of five 

 millimetres beneath the stage. Air-bubbles in 

 water and Canada-balsam respectively may be 

 examined in a drop or two of either liquid, placed 

 upon a slide with a thin cover super-posed, after 

 vigorously shaking the bottle containing it. A 

 drop of oil or turpentine coloured with magenta or 

 carmine, and a drop of water, may be placed on a 

 slide together, covered, and the cover moved about 

 to cause them to mingle. Globules of oil in water 

 may be studied in an emulsion prepared by 

 shaking the two together with a little powdered 

 gum. In an air-bubble in water, when focussed, 

 the centre of the image appears very bright, and it 

 is surrounded by a greyish zone, which in turn is 

 encircled by a broad black ring interrupted by one 

 or more brighter ones. On focussing downwards 

 the bright centre becomes smaller and brighter, 

 and is sharply divided from a very broad, black 

 ring which has bright diffraction circles outside. 

 An oil globule in water shows the central disc 

 brightest when the upper part is in focus, and the 

 broad black outer circle is not surrounded by 

 diffraction rings. Focussing down to the middle 

 of the globule the disc becomes very large, but is 

 much less bright, and the narrow, black encircling 

 ring is bordered by diffraction circles both within 

 and without. 



