18 



HARDWICKE'S SCIENCE-GOSSIP. 



MICROSCOPY. 



Crystals of Lime in the Pkawn's Skin. — 

 The skin of the Prawn consists of three layers ; be- 

 tween the outer and middle coats the crystals of 

 carbonate of lime appear to lie. In a cast skin no 

 crystals seem to be ever found, nor do any appear 

 in a newly-formed skin. What then becomes of 

 these crystals ? Does the water dissolve them, or 

 does the new skin absorb them in order to con- 

 solidate it? Perhaps some reader of Science- 

 Gossip may be in a position to answer the above. — 

 F. B. KyngdoH. 



On Preserving and Mounting Fresh-avater 

 Alg^. — The fresh-water algse are not only beau- 

 tiful but easily procurable, and would no doubt 

 have received a much larger share of attention from 

 the microscopist were their preservation as per- 

 manent objects possible. In the majority of instances, 

 the beautiful colour and arrangement of the endo- 

 chrome is destroyed by the death of the organism ; 

 there are some forms, however, which retain a con- 

 siderable amount of their pristine beauty after 

 having been mounted many years. The Nostocs 

 are but little changed when mounted in fluid; and the 

 Desmids, although losing their vivid green colour, 

 retain their elegant outlines. The plan proposed 

 by Dr. H. Wood* for the preservation of the fresh- 

 water algse, according to the author, has given tlie 

 best results hitherto obtainable. After cleaning 

 them, which he accomplishes in the following way : 

 — " The large filamentous ones may be washed by 

 holding them fast on the slide with a bent needle 

 or a pair of forceps, and allowing water to flow over 

 them freely whilst they are rubbed with a stifBsh 

 camel-hair brush, or the mass of specimens may be 

 put into a bottle half-filled with water and shaken 

 violently, drawing off the water from the plants, and 

 repeating the process with fresh additions of water 

 until the plants are well scoured. I find, after trial 

 of acetate of ammonia and various other media, 

 that a very weak solution of carbolic acid is the 

 best possible fluid to mount these plants in " — 

 the difficulty of securing eifectually fluid-mounted 

 forms induced Dr. Wood to try the following plan. 

 He makes a solution of gum-damar in benzole, to 

 which previously triturated oxide of zinc is added. 

 This cement should be of such consistency as to flow 

 freely from the brusli. It will adhere if washed 

 properly when the cell-cover is pressed down, even 

 when glycerine is used as the preservative medium. 

 Its advantage lies in the circumstance that the 

 glass cover can be placed upon the ring of it whilst 

 still fresh and soft, and that in drying it adheres 

 to both cover and slide, so as to form a joint be- 



* " A Contribution to the Natural History of the Fresh- 

 water Algae of America." By Dr. H. Wood. 



tween them of the width of the ring of cement. 

 The method of mounting with it is as follows : — A 

 ring of it is made, by means of a " turntable," on a 

 slide, which is put aside to dry. When required 

 for use, the slide is again placed on the turntable, 

 and a new ring of cement put directly over the old 

 one. The specimen is immediately within the cell, 

 and the requisite quantity of carbolated water 

 added. The cover, which must be large enough 

 to entirely or nearly cover the cement ring, is now 

 picked up with the forceps, the under-side being 

 moistened by the breath, to prevent adhesion of 

 air-bubbles, and placed carefully in position. It is 

 now to be carefully and equably pressed down with 

 some force. By this any superfluous water is 

 squeezed out, and the cover is forced down into 

 the cement, which rises as a little ring around the 

 edge. The slide may now be put aside to dry, or 

 better, an outside ring of cement run round it in 

 the usual manner. Unfortunately, the author does 

 not state the length of time he has used this 

 method. My experience of soft cements is that in 

 a shorter or longer period they almost invariably 

 run in, and 1 much fear gum-damar will not prove 

 an exception.— i^. K. 



On Mounting Microscopic Objects.— We beg 

 to draw the attention of our microscopic readers, 

 who are always interested in anything relating to 

 the mounting of objects, to the second edition of 

 Davies's little book on this subject, which has just 

 been issued by Hardwicke, Piccadilly. This edition 

 is considerably enlarged; and, as its author was 

 too unwell to see the sheets through the press him- 

 self, this edition has been edited by Dr. Matthews, 

 to whom Mr. Davies handed over his additional 

 notes, &c. A prefatory chapter has been added* 

 and such extensions made as will introduce the 

 book to a new class of readers— the medical students 

 and practitioners. The editor has done his work 

 well, and we can now confidently recommend this 

 able little book as the cheapest and most compre- 

 hensive which the young miscroscopist can obtain. 



BOTANY. 



Plant Crystals.— Professor Gulliver, referring 

 to his descriptions and figures of Raphides, Sphajra- 

 phides, and long crystal prisms, given in Science- 

 Gossip, May, 1873, continues his researches in a me- 

 moir, illustrated with a plate containing ten figures, 

 in the Monthly Microscopical Journal, Dec, 1873. Of 

 this last paper, the subject includes observations 

 " on the crystals in the testa and pericarp of several 

 orders of plants, and in other parts of the order 

 Leguminosaj." These crystals he names " short 

 prismatic crystals," in order to distinguish them 

 from the other and very distinct forms mentioned 

 above. The short prismatic crystals are constantly 



