_ January 6, 1923] 
NATURE 15 

various organisms—present in the sea-water—which 
give rise to the unpleasant smell. The principal 
organisms concerned would appear to be the well- 
known anaerobic bacteria which produce hydrogen 
sulphide. 
The cause of chambering among oysters on beds 
in high estuarine situations can therefore be stated 
to be the reduction in bulk of the body, which occurs 
at the shell-growing period in these situations from 
a variety of causes, of which the decrease of bulk 
due to breeding and salinity variations are the most 
important. 
It may be noted, however, that chambering is rare 
on what are regarded as good oyster beds, and there 
is good reason to believe that the salinity variations 
over such beds range between about 30 and 34 per 
mille. 
Chambering has also been observed in some deep- 
sea oysters, and, it may be presumed, from the opera- 
tions of the same causes as in high estuarine situations. 
The conditions on deep-sea oyster beds are very 
different from those in high estuarine situations, 
but the breeding phenomena on the former beds 
are not known. It seems probable that breeding 
may not occur at all in some years in deep-sea beds, 
or that there is only a short breeding period (see 
Orton, Journ. Mar. Biol. Assn. vol. 12, p. 343), but 
that on the other hand growth is probably con- 
tinuous over the greater part of the year. Since 
salinity variations would not be great on deep-sea 
beds it would appear that the reduction in bulk 
of the body due to breeding coincident with extensive 
shell-growth (see Hoek, Report on the Causes of 
the Deterioration in Quality of the Zealand Oyster, 
p. 90, s’Gravenhage, 1902) is the main cause of 
chambering in deep-sea oysters. 
The view given above on the cause of chambering 
in oysters could readily be put to the test of experi- 
ment, but it would be preferable to carry out experi- 
ments on a large scale, beginning with thousands 
of young oysters. The economic importance of 
oysters is sufficiently great for the matter to be taken 
up by such large oyster-planters as are troubled with 
chambering. It will readily be seen from the argu- 
ment given above that chambering is a minor patho- 
logical phenomenon, and that there is nothing to 
prevent the growth of a good well-fished oyster in 
a chambered shell, and, as a fact, excellent oysters 
do occur in chambered shells. 
EpitH Worsnop. 
J. H. Orton. 
Marine Biological Laboratory, 
Plymouth, December 4. 

The Hardness of Vitreous Silica. 
TuE hypothesis proposed by Sir George Beilby to 
account for the hardening of metals by cold-working, 
and accepted by most metallurgists in this country, 
assumes the production of a vitreous phase of the 
metal by the breaking down of the crystalline struc- 
ture during extensive deformation. It requires that 
the vitreous modification of a substance should be 
harder than the crystalline. Direct evidence on this 
point has rarely been obtained. Silica, however, 
suggests itself as a suitable substance for such a test, 
both the crystalline forms and the under-cooled glass 
being readily obtained in a form suitable for mechan- 
ical tests. The hardness of silica was carefully 
studied by Auerbach, who found a surface of vitreous 
silica to be less hard than either of the principal faces 
of quartz. Most commercial silica glass is, however, 
so weakened by the presence of numerous gas bubbles 
that any grinding test is likely to give low results for 
the hardness. 
“NO. 2775, VOL. III] 
We have recently had the opportunity of examining 
a specimen of silica of unusual hardness. This was 
obtained by throwing a quantity of pure quartz sand 
on to the slag in an open-hearth steel furnace when the 
slag surface was at an exceptionally high temperature 
(1800° C. by the optical pyrometer). The sand melted, 
and formed a lenticular mass, which only mixed with 
the slag at its margin. On removing the product, a 
colourless, translucent mass of glassy silica was 
obtained, passing sharply into the dark slag. Analysis 
of the colourless mass gave 97-7 per cent. silica, 2-0 
per cent. lime, and a trace of iron. A thin section 
between crossed Nicols was isotropic, with only a few 
scattered inclusions of minute crystals and some 
spherical bubbles. 
Tests with a sclerometer, using a diamond point 
under a load of 400 grams, gave a broader scratch on 
a prism face of quartz than on a polished surface of 
the vitreous silica, but on account of the splintery 
nature of both scratches little reliance could be placed 
on the actual measurements. A fractured edge of 
the fused product distinctly scratched the prism faces 
of quartz, while natural angles of the latter failed to 
scratch the vitreous surface. Further tests were made 
with the scleroscope, an instrument in which the 
rebound of a diamond-pointed hammer falling from 
a height is measured. The following figures were 
obtained, all the specimens being embedded in pitch 
in the cast-iron cup provided with the instrument : 
Polished vitreous silica . a 3 - O94 
Ouartz; prismiface 7 & se is = a 
Commercial vitreous silica . 3 23 62 
The experiments are not conclusive, and a higher 
accuracy will be attempted, but it would appear that 
silica thoroughly fused at a high temperature is dis- 
tinctly harder than crystalline quartz, and to this 
extent the experiments support Beilby’s hypothesis. 
Cosmo ,JOHNS. 
Cecit H. DeEscu. 
Sheffield, December 2. 

Distribution of the Organ-Pipe Diatom, 
Bacillaria paradoxa. 
In the Notes in Nature for September 29, 1921 
(vol. 108, p. 163), it is mentioned that Mr. J. W. 
Williams and Mr. H. Weaver have found the curious 
organ-pipe diatom, Bacillaria paradoxa, in canals and 
pools in Staffordshire and Worcestershire. It may 
be of further interest to note that while leading a 
party of field naturalists on a seaside expedition to 
Altona Bay, near Melbourne, some years ago (Vic- 
torian Naturalist, vol. xxxiv., June 1917, p. 16), we 
found this same diatom very abundantly both in the 
sea and up the Kororoit Creek for a good distance, 
where the water was only slightly brackish. On 
examining the finds at home I was struck with the 
fact that, whereas the marine form was very active 
in its peculiar sliding movement, the brackish form 
was sluggish in contrast. It would be interesting to 
know whether other observers have found the fresh 
water to act as an agent for ‘‘ slowing down.”’ Prob- 
ably the saline conditions of the water assisted the 
osmotic pressure which may induce the movement. 
F, CHAPMAN. 
National Museum, Melbourne, 
October 24. 

Speculation concerning the Positive Electron. 
Sir OLivER LopGe’s interesting speculation, in 
Nature of November 25, p. 696, as to the possible 
similarity of positive and negative electrons suggests 
an inquiry into the relative abundance of the lighter 
