504 



NATURE 



[October 19, 1S93 



I found that the liquid gradually penetrated into and 

 filled the canals which were open. Fig. 4 shows the 

 central parts of crystals with canals partly filled with the 

 coloured liquid. Near the centre small air-bubbles are 

 still visible. Fig. 6 is the central part of a star powerfully 

 magnified. The interesting structure may be judged by 

 the photograph. 



Phenomena attending the Compression of Snow Crystals. 

 — A stellate plate was slowly compressed by screwing 

 down the objective upon the cover-glass. After this 

 pressure it was still entire. In the interior of the 

 crystal new curvilinear figures or pressure lines had 

 appeared, following a regular course analogous to that 

 of the organoid figures. This analogy suggests that the 

 latter may possibly be explained as tensional phenomena. 



Exceptional Symmetrical Conditions. — The fine cavities 

 in the centre of the stars are sometimes regularly ar- 



FiG. 6. 



ranged after only /zf/f? symmetrical planes at right angles 

 to each other and of different value (see Fig. 4), in ac- 

 cordance with the symmetrical conditions that we find 

 in crystals belonging to the orthorhombic system. 



Hoar-frost. — In addition to the photographing of snow 

 crystals, I have also examined and reproduced by photo- 

 graphy crystals of hoar-frost deposited on window-panes. 

 Even these crystals formed often hexagonal tables, but 

 were entirely without the remarkable cavities observed in 

 snowflakes. 



The investigations of which I have here given a brief 

 account show that the structure of snow crystals is very 

 complicated, and display several peculiarities which, so 

 far as we know at present, are unexampled in other 

 crystals. I hope to be able to resume these investiga- 

 tions next winter on a more extensive scale, in order to 

 obtain, if possible, a complete elucidation of the interest- 

 ing phenomena alluded to in the present paper. 



G. NORDENSKIOLD. 



BUTSCHU'S ARTIFICIAL AM(EB.-E.^ 



PROF. BUTSCHLI, of Heidelberg, so well known 

 by his valuable work on the Protozoa, and his 

 contributions to Bronn's " Klassen und Ordnungen," has, 

 in the monograph under review, approached a subject 

 of deep interest and great difficulty, namely, the cause 

 of protoplasmic movement. His researches in this 

 direction are already known to readers of the Quarterly 

 Journal of Microscopical Science, for in 1890 Prof. 

 Lankester inserted a letter from Prof. Biitschli, in which 

 the latter gave a short account of his experiments. In 

 the present monograph his researches are given in a 



' " Untersuchunfcen ubermikroskopischeSchaumeund das Protoplasma." 

 Von O. Biitschli. (Leipzig : Wilhelm Engelmann, iSya.) 



NO. I 25 I. VOL. 48I 



completed form and in great detail. The gist of the 

 whole subject may be put as follows: — Prof. Biitschli 

 makes an artificial oil and water emulsion in a way sug- 

 gested by Nuincke, and finds that under certain conditions 

 drops of this emulsion exhibit streaming movements and 

 changes of shape : according to Prof. Biitschli, proto- 

 plasm is itself a natural emulsion, and the streaming 

 and amoeboid movements of protoplasm are, like those 

 of the artificial emulsion, due to surface tension. 



Working at emulsions, Nuincke had previously found 

 that if substances soluble in water be finely powdered 

 and rubbed up with oil, and the oil subsequently sur- 

 rounded with water, the latter diffuses into the oil, which 

 it converts into a foam or emulsion of little water drop- 

 lets closely packed together in the oily matrix. The 

 emulsion may obviously be compared with the sea-foam, 

 in which we find air globules closely packed in a water 

 matrix, the oil in the emulsion and the water in the sea- 

 foam having an alveolar or honeycomb build or form. 

 The Nuincke emulsion is obviously, too, the reverse of 

 the emulsions made by Johannes Gad with weak 

 K2CO3 and oil, in which the oil droplets lie closely 

 packed in a water matrix ; it is also the reverse of the 

 numerous emulsions made every day by the druggist 'vho 

 uses oil in mucilage, malt-extract, &c. When Biitschli 

 first tried the Nuincke method he used common salt, 

 sugar, and nitre, taking these as examples of substances 

 readily soluble in water. He succeeded, however, better 

 by using Na.,C0:5, of K2CO3, and proceeded as follows. 

 The salt, preferably KXO3, was obtained pure and dry, 

 and was finely powdered in an agate mortar. He then 

 breathed upon it until it was slightly moist, and rubbed it 

 up with olive oil until a thick white paste was formed. 

 A tiny drop of the paste was then placed on the centre of 

 a cover-glass, and inverted over a drop of water, and in 

 order that the drop might not be pressed out of shape by 

 the weight of the cover, the latter was supported by little 

 pellets of wax or paraffin. The preparations so obtained 

 were placed on one side in a damp chamber for twenty- 

 four hours, and then washed out with water by inserting 

 a piece of blotting-paper into the chink between the slide 

 and cover, and supplying fresh water at the opposite side 

 of the cover by means of a pipette. The water was then 

 replaced by equal parts of glycerine and water, after 

 which the drops of emulsion became clear and trans- 

 parent, exhibiting changes in shape and streaming move- 

 ments very much like those of an amoeba. It appears 

 that the consistency of the olive oil is- a very important 

 factor in determining the successful issue of one of these 

 experiments. Ordinary oil is of no use, it must be kept 

 for some time in an open vessel, though the time may be 

 shortened by keeping it in a hot-air chamber at So°C. 

 and testing the oil from day to day. It must be thick 

 and viscous, but not too much so. 



When examined by the aid of a microscope the emul- 

 sion appears as a network of oil enclosing the water 

 droplets, for the structure is, of course, seen in optical 

 section. Curious streaming movements may be observed 

 within the emulsion, and these may continue for hours ; 

 movements of the drop as a whole occur, and always 

 in the direction of the stream. If the emulsion drop be 

 carefully watched it will be seen to change its shape, and 

 to throw out processes — which, by the way, are always 

 ciub-shaped — and to withdraw others. Up the centre of 

 these processes a streaming movement takes place, and 

 the streams at the tops of the processes spread out and 

 flow back in a layer next the surface. These movements 

 are influenced by warmth and electricity, and we have, 

 therefore, in these Biitschli's drops something which 

 might deceive one into supposing that actual amcebse 

 were in the field of observation. 



The movements of the oil emulsion are due, no doubt, 

 to changes in the surface tension of the fluids in contact 

 with each other, Biitschli's case being an illustration of 



