450 



;XO\VLEDGE. 



XOVEIIBER. 1911. 



Rubidium likewise emits a less penetrating radiation, but 

 caeciuin, which is so akin to rubidium chemically, does not 

 appear to do so. unless such particles arc niovini; too slowly 

 to be detected. 



Kadio-activity has now developed to such an extent that the 

 knowledge of its processes leads it now to he applied to the 

 elucidation of many problems of a less specialised character. 

 Professor Rutherford has recently thrown much light on the 

 structure of the alom. by a theoretical investigation of the 

 .action of the o and ,i particles penetrating an atom, while 

 his theoretical deductions are well backed up by the ex- 

 periments of Geiger and Marsden and Crowther. Mr. 

 Marsden is likely to give to readers of " Knowledgk " 

 an account of this work, and I will therefore only indicate 

 the nature of Rutherford's theory. He starts by assuming 

 the atom to consist of a central nucleus with a charge 

 C(iual to the number of electrons multiplied by the charge on 

 each (4-65 X 10"'" electrostatic units), while there is an outer 

 shell carrying an equal and opposite charge. He investigates 

 what would happen it an a particle la positively charged atom 

 t>f heliumi emitted, say from Radium C. were to penetrate 

 such an atom, and what the chance would be for a large 

 deflection of such a particle. He finds that when the a particle 

 penetrates very close to the central nucleus, its deflection will 

 be very large and it may be deflected 150° or so, back towards 

 the direction in which it came. It appears from experiments 

 on the percentage of particles deflected at various angles, or 

 measured by the number of scintillations occurring in unit 

 time on a zinc sulphide screen placed to receive them, that 

 the number of large deflections is greater than would be given 

 by an atom of such a character that the large deflections 

 would be made up of a number of smaller deflections. This 

 effect no doubt does occur to some extent, and especially with 

 the lighter (i particles, which, although moving more rapidly, 

 do not possess so great energy as the a particles. Professor 

 Rutherford's theory of the central condensed charge in the 

 atom explains well the experiments on the diffuse reflexions of 

 a particles, on the variation in the percentage deflection at 

 different angles with the atomic weight of the reflecting atoms, 

 on the average scattering of the rays produced in penetrating 

 thin plates of various metals, and on the scattering of ii rays 

 of different velocities by atoms of different weight. The outer 

 charge of the atom is probably that of a number of electrons 

 moving as satellites to the central charge. This idea is similar 

 to the theoretical idea of the atom worked out by Nagaoka. 

 which was something of the nature of a minute planet Saturn. 

 It is likely that this scintillation work will give much informa- 

 tion on the structure of the atom. The problem is akin to 

 that which would present itself to a philosopher living outside 

 the solar system, and who wished to investigate the structure 

 of it by the orbit and perturbations of a comet passing through 

 the system. But in our case the comet or a particle is more 

 under control. 



ZOOLOGY. 



By Pkoikssok J. Arthl'K Thomson, M..\. 



THE LIVING EARTH.— It has been shown by Drs. 

 Russell and Hutchinson, of the Rothamsted laboratory, that 

 soils heated or treated with certain volatile antiseptics, and 

 brought again under conditions favourable to plant growth, 

 show a great increase in fertility. The soil bacteria are 

 first reduced in numbers and then they increase enormously. 

 To this increase is due an increase in the production of 

 ammonia in the soil, and to this the greater fertilit\'. But 

 why should the decrease of bacteria be followed by their great 

 increase ': 



To explain this it has been suggested by the authors named 

 that the treatment with volatile antise|)tics kills off the 

 protozoa of the soil, some of which feed on bacteria, and 

 thus limit their increase. The protozoa arc more susceptiblc- 

 Ihan the l)acteria to the sterilising agents. When they are 

 killed off the bacteria multiply without this check. But our 

 knowledge of the protozoa of the soil is someuh.it scanty and 

 vague. 



\\"e welcome therefore a recent investigation by Mr. T. 



Goodey. in which he names about thirty protozoa found in 

 cultures of soil. Ivighteen of these are ciliated infusorians. 

 and in regard to these Mr. Goodey comes to the interesting 

 and important conclusion that they exist in the soil in an 

 encysted, not in an active state. " In consequence, they 

 cannot function as the factor limiting bacterial activity in the 

 soil." 



HOW LONG DO WHITE MICE CARRY THICIR 

 VOUXG? — One would have thought that a simple (juestion of 

 this sort admitted of ready answer. The usual statement is 

 that the period of gestation is twenty-one days, the same as the 

 period of a chick's development. But J. Erank Daniel reports 

 that there is great variability in the duration of the period — 

 in different mice and in the same mouse. I'or non suckling 

 mothers a definite gestation period of practically twenty days 

 may be stated : and this holds true irrespective of the size of 

 the litter. But for suckling mothers there is great variability, 

 from a minimum of twenty-two days to a maximum of thirty 

 days. .-Xnd it seiuns that the period of gestation in suckling 

 mothers varies directly with the number of young suckled. 

 The "how" of this relation, if it is a well-establislied relation, 

 remains uncertain. 



BITEOE HEU )DERMA.— The virulence of the venom of 

 the Gila Monster, the poisonous lizard of Mexico and Arizona, 

 has been often proved in the case of small animals, but we 

 have little precise knowledge of the effect of the poison on 

 man. This gap has been filled by the careful observations of 

 Mile. Marie Phisalix. who was accidentally bitten while 

 examining the lizard's mouth. She describes the intense 

 pain, the swelling, the profuse perspiration, the giddiness, and 

 other disagreeable results of the bite. Even after a week the 

 fatigue, the giddiness, and the local pain had not disappeared, 

 but no serious consequences ensued. 



SLOWING DEVELOPMENT OF HERRINGS' EGGS. 

 — One of the methods suggested in order to secure the intro- 

 duction of the herring into New Zealand waters is that of 

 lengthening out the period of embryonic development, so that 

 transportation of the eggs may perhaps be effected before 

 hatching occurs. Dr. H. Charles Williamson was able some 

 time ago to lengthen out the period of embryonic development 

 to fifty days. He did this by lowering the temperature, which 

 probably makes the formation of nuclein-compouuds slower, 

 and therefore retards cell-division. His further endeavours 

 to extend the period have not been successful. Lowering the 

 temperature still further slows the development so unich that 

 it is very apt to stop altogether. 



THE HIBERNATING SNAIL. — It is interesting to 

 connect the internal and external periodicities, and there is 

 a great deal of interesting work to be done in comparing the 

 details of organic structure at dift'erent times of year. Taking 

 the common Helix poiuatia, Spiro has recently shown that 

 the granules and drops of fat which are abundant in the 

 summer in the cylindrical cells lining the alimentary canal 

 are all gone in winter ; that the nuclei of these cells become 

 poorer in chromatin : that the cilia which all the cylindrical 

 cells have are lost. There is another kind of cell in the lining 

 membrane, vase-like in shape, which secretes nmcus in 

 summer during digestion, but, of course, ceases to do so 

 when hibernation sets in. We thus get the impression of 

 the depth of the organism's reaction to the seasons. It is 

 also very interesting to find that the whole lining of the 

 alimentary canal is renewed in spring before the nutritive 

 period of the year re-commences. 



H.ABITS OE SCUTIGERA.— J. Kunckel d'Herculais 

 has been studving the well-known long-legged centipede called 

 Sctitigcra colcopfrafa which is common in houses. It is 

 famous for the disproportionately long limbs, fifteen pairs in all, 

 for its compound eyes, .and for many other peculiarities, but 

 what Kunckel d'Herculais calls attention to is its activity 

 as a fly-catcher, DLiriug the day it lies quiet in crevices 

 about the doors and windows and flooring, .At night it goes 

 on the hunt and kills large numbers of flies, e.g.. Fannia 

 scalartH. It throws itself upon the fly, enwraps it in its 



