SCIENCE-GOSSIP. 



187 



Preparation of Micro-Sections of Lignite. — 

 As a rule the intense blackness of lignite, even in 

 the thinnest of sections, is a serious obstacle to a 

 satisfactory examination under the microscope. 

 To make a successful study with higher powers 

 the specimen must be thin enough to be viewed 

 by transmitted light. It is not often that such 

 sections can be obtained by grinding in the manner 

 usually adopted for cutting rock-sections, for even 

 when the sections are so thin as to break into 

 fragments and be torn from the slide they still 

 remain too opaque for even a ray of light to pass 

 through. Other processes, such as incineration, or 

 boiling in acids, are equally unsuccessful. The 

 method that is best adapted for such materials 

 is that which is recommended by Griffith and 

 Henfrey, in their " Micrographic Dictionary," for 

 the examination of coal. If any of our readers 

 know of equally successful methods we shall be 

 glad to hear of them. 



Micro-Photography Simplified. — The delinea- 

 tion of microscopic objects by means of photo- 

 graphy has of late years become very popular 

 with a considerable sections of microscopists. 

 There is still a large number who hesitate to take 

 up this useful and instructive branch cf micro- 

 scopy, and this not so much for the few difficulties 

 that the subject pre- 

 sents, as on account 

 of the mistaken no- 

 tions that they have 

 regarding the cost of 

 an equipment. For 

 the best results with 

 the least expenditure 

 of time a camera spe- 

 cially designed for 

 micro -photography 

 is desirable ; but it 

 is not by any means 

 necessary for doing 

 good work. Through 

 the courtesy of Mr. 

 J. Browning, of the 



Strand, London, we have recently had an op- 

 portunity of trying a micro-photographic camera 

 which, while doing effective work, quite overcomes 

 the difficulty of those who hesitate about taking up 

 micro-photography on the score of expense. The 

 complete apparatus consists of a mahogany camera 

 weighing, with an internal flap shutter, about six 

 and a-half ounces, a focussing screen and a ma- 

 hogany double-dark slide. It is one of the smallest 

 micro-photographic cameras we have seen, and it 

 is a perfect combination of compactness, portability 

 and lightness. The mode of attachment to the 

 microscope is shown in our illustration. From a 

 personal experience we can vouch for the fact that 

 it is capable of doing fairly critical work, and it is 

 therefore specially suitable for students in the 

 photographing of botanical, entomological and 

 histological specimens. Its cost, 16s. 6d., brings 

 it within the reach of all. 



Measurement of Cotton Fibres. — Each 

 individual hair of cotton seed is known com- 

 mercially as a cotton fibre. As seen under the 

 microscope each such hair has a blunt point, the 

 natural termination of the fibre, differing from its 

 opposite extremity, which shows the fracture 

 occasioned in picking and ginning. To measure 

 these fibres for the purpose of estimating their 

 quality the cotton expert first mixes and then 

 loosely pulls apart a few ounces of cotton, and 



draws out of this, at random, one fibre, which he 

 places on a glass slide previously moistened with a 

 little weak gum water. The fibre is then gently 

 and carefully smoothed with a camel's-hair pencil 

 and the fingers until straight. This is accom- 

 plished under a dissecting microscope with low 

 powers. When straightened the fibre is viewed 

 with the compound microscope, using a magnifying 

 power of about 400 diameters, in order to ascertain 

 whether its natural point is present. If wanting, 

 which is exceptional, the fibre is discarded. A 

 glass micrometer, two and a-half inches long, 

 divided into thirty-seconds of an inch, the lines 

 ruled so as to be visible through the glass, is then 

 placed over the slide holding the fibre and its 

 length ascertained by close and careful inspection. 



Reproduction of Bacteria. — There are two 

 methods by which bacteria are reproduced : first, 

 by fission, that is, simply splitting or dividing in 

 half, each new half living and dividing in turn ; 

 the second method is by spore formation. Alluding 

 to these modes of reproduction, Mr. L. Atkinson, 

 in a recent lecture, attempted, by calculation, to 

 estimate the rate of increase of these minute forms 

 of life. Assuming a germ divides into two within 

 an hour, then again into eight in the third hour, 

 and so on, the number in twenty-four hours would 



exceed sixteen and 

 a-half millions. Now 

 forty thousand mil- 

 lions will only weigh 

 one grain, yet after 

 twenty - four hours 

 the descendants of 



Micro-photographic Camera. 



one organism, assum- 

 ing the necessary 

 food and space could 

 be supplied, would 

 weigh ssVjfth of a 

 grain, after two days 

 one pound, and in 

 three days 7366 

 tons. Of course, 

 these figures are 

 theoretical, and could only be realized if there 

 were no conditions to prevent this incomprehen- 

 sible increase. Fortunately overcrowding is as 

 fatal to microbes as to the human race. 



Glycerine-Gelatine. — After referring to the 

 difficulties met with when objects are mounted in 

 pure glycerine. Professor A. M. Edwards gives, in 

 the columns of the. "Natural Science Journal," 

 some results of the experiments that he has made 

 in the use of glycerine-gelatine. His experience 

 with the mixture has been a favourable one. The 

 preparation is made as follows. Take a sufficient 

 quantity of fine gelatine, break it up, cover with 

 cold water and allow it to stand all night. Next 

 morning pour the water off and warm the gelatine 

 in a steaming-pan. When melted add to it a suffi- 

 cient quantity of strong glycerine. The quantity 

 used varies according to the nature of the speci- 

 mens to be mounted, but one part of glycerine to 

 five parts of gelatine is an average mixture. 



To Correspondents. — I shall be glad, when 

 possible, to reply to correspondents on micro- 

 scopical subjects through the post, but in such 

 cases a stamped addressed envelope should be 

 enclosed. My address will be found- at the head 

 of these columns. I have recently received some 

 sketches made with lead pencil. These are useless 

 for reproduction. A good black aniline dye or 

 Indian ink should be employed. 



