14 NATURE 
[JANUARY 6, 1923 


necessary in the laboratory in order that the blue 
opalescence due to internal scattering may be satis- 
factorily observed, that is, that the ice should be of 
the maximum clearness and transparency ; in either 
case, air-bubbles, striz, and other inclusions obscure 
the effect sought for. The inference that the pheno- 
mena arise in the same way seems legitimate. 
I am aware that a different explanation of the 
colour of natural ice has been put forward by Tyndall 
and other writers, that is, that the colour is simply 
an absorption effect. To me, however, it appears 
that the latter view presents fundamental difficulties. 
Prima facie, no substance can exhibit colour im its own 
body except as the result of internal diffusion or scatter- 
ing. Colour due to simple absorption can only be 
perceived when a luminous object is viewed through 
the substance, and even then it is the source, not 
the absorbing medium, that appears coloured. 
The absorption theory thus leaves it unexplained why 
clear ice should exhibit any colour at all. Indeed, it 
would appear that the colour of ice is often very con- 
spicuously observed when the light traversing it has 
no chance of reaching the observer’s eye directly. 
Thus, for example, in his lecture on ice and glaciers, 
Helmholtz describes very vividly the experience of 
the Alpine traveller who, traversing the broken surface 
of the glacier along a narrow ridge, looks down into 
the crevasses on either side’and views with mixed feel- 
ings of pleasure and awe their dark blue walls going 
down to the depths. It is obvious that in sucha case 
as this, the light filtering down into the solid mass of 
transparent ice forming the glacier through the super- 
ficial layers or otherwise, has no possibility of return- 
ing to the observer above except as the result of 
internal scattering. 
The ‘natural view to take is therefore that the blue 
opalescence is the real cause of the colour of transparent 
ice observed under such conditions, the absorption of 
light in traversing the medium tending merely to 
diminish its intensity and make it of a more saturated 
hue. C. V. RaMan. 
210 Bowbazaar Street, Calcutta, 
November 9. 

The Cause of Chambering in Oysters 
and other Lamellibranchs. 
THE phenomenon of chambering in oysters and 
other lamellibranchs is well known, and in oysters 
is a source of much financial loss to some oyster 
planters. In a chambered oyster one extensive 
closed chamber or several superposed large chambers 
may occur enclosed within the shell substance— 
usually in the convex valve, but sometimes in both 
valves. The chambers are separated from each 
other or from the body of the oyster by thin brittle 
partitions of shell only, and contain usually an evil- 
smelling liquid. 'Whenachambered oyster is opened, 
great care is required lest the brittle wall of the 
chamber be broken and the evil-smelling liquid 
released on the oyster, which would in that case be 
rendered unfit for eating. 
The cause of chambering has recently been described 
by Houlbert and Galaine (Comptes vendus, Acad. Sci. 
Paris 162, 1916), not as “‘ un accident pathologique 
.’ but “comme la persistence d’une propriété 
ancestrale.’’ Later, these writers suggest inanition 
as a cause. In our recent investigation on oysters 
we have observed several phenomena which when 
pieced together offer a rational explanation of 
chambering as a minor pathological phenomenon due 
to varying external conditions coincident with varia- 
tions in the internal condition of oysters. 
We have observed that when oysters are kept in 
bell-jars or dishes in a warm room in the laboratory 
NO. 2775, VOL. 111 | 
without food in winter they begin to grow shell 
automatically, whereas in the sea in a normal winter 
no growth of shell occurs; moreover, oysters kept 
in the laboratory in summer may continue to lay 
down shell at a rapid rate although food is practically 
absent. In such oysters it frequently happens that 
owing to the unfavourable conditions of transport 
in summer weather the oysters arrive in a bad condi- 
tion, one of the effects of which—combined with the 
effect of the laboratory water—is to cause the oysters 
to shrink somewhat in their shell, but especially 
to contract the mantle, whereby puckers are formed 
in it. Now, although the mantle and body shrink, 
the layer of the mantle and body next to the shell 
continues to secrete shell substance in a thin layer. 
As a consequence of these conditions the oysters lay 
down on the inside of the shell a thin layer of shell- 
substance in an irregular manner, following especially 
the puckerings of the mantle. This thin layer of 
shell is laid down with a water space between it 
and the shell, and is, in fact, a small chamber. The 
same process occurs, as is well known, when mud 
gets into the shell accidentally, or when a hole is 
punctured in the shell and is afterwards plastered 
over with repair shell inside. The above facts show 
that shell is laid down automatically by the mantle 
and body surface adjacent to the shell if the tempera- 
ture is sufficiently high and—-it may be added— 
if the oyster is in reasonably good condition. 
The second observation is well known to oyster- 
cultivators, namely, that oysters will swell consider- 
ably in water of low salinity and shrink in water 
of high salinity. This change occurs probably 
through the readiness of the bladder-tissue in 
lamellibranchs to respond and accommodate itself 
to changes in osmotic pressure. Now, chambered 
oysters occur most commonly on beds in high 
estuarine or riverine situations, where the salinity 
variations are great. The third factor of interest 
in this. problem is that oysters vary greatly seasonally 
in weight, and, it can be safely deduced, in volume 
as well: very low salinities due to heavy rains 
would certainly also reduce the amount of available 
food-material for oysters. We have also observed that 
when oysters are kept for some months in tanks in 
stagnant water, the salinity of which thereby increases 
considerably, the percentage of chambered oysters 
is afterwards found to be very high and the bodies of 
the oysters shrink to a very great extent. The last 
factor of importance is this, that the rainy period in 
England falls either in the early part of the year or at 
the end of the year, while the month of May is 
fairly dry; but in May and June oysters prepare 
or begin to breed, and it becomes warm enough nor- 
mally for shell to grow. 
These observations may now be pieced together. 
In the early months of the year in high estuarine 
or riverine beds oysters are frequently subject to 
low salinities, e.g. 15 per cent. or even lower; to- 
wards May or June higher salinities will generally 
occur in these situations together with the onset 
of breeding among oysters; both these factors 
tend to reduce the volume of the body of the 
oyster, and—it has been noted—at a time when 
it is warm enough for shell-growth to take place. 
If the oyster is in good condition, shell-growth 
—it has been observed—occurs automatically. Thus, 
as the volume of the oyster is shrinking in these 
situations, shell material is being produced, con- 
sequently a shell lamina which is not adjacent to 
the existing body of the shell is laid down and a 
chamber results. Water probably forms in the 
chamber by percolation along the outside of the 
body of the oyster between the body and the shell. 
In this way are probably included in the chamber 
