810 

species is not well known; but it is cited from the 
Pliocene. I am dealing with its supposed occurrence 
at the Cape in a forthcoming paper. 
The presence of the essentially Austral forms, 
Magellania lenticularis and Magadina cumingi, in the 
Tertiary rocks of Japan, opens up a very wide 
question as to the former geographical distribution 
of these genera. With regard to the first species, I 
might point out that the figures accompanying the 
memoir do not suggest the New Zealand form ; 
figure 17 especially being very unlike. 
As to Magadina cumingi, the figures certainly 
present a general resemblance to the species occurring. 
off the coasts of S.E. Australia and to certain New 
Zealand Miocene forms. But identity in outward 
appearance is not a safe criterion. It is found by 
experience that it is necessary to investigate the 
interiors before a species can be definitely referred 
to its proper genus. Forms having the same shape 
externally may possess quite different loop-stages. 
This feature is nowhere better displayed than in the 
forms possessing Bouchardiform beak characters, like 
the species in question. 
In conclusion I should like to point out that Dall’s 
generic name for T. grayi Reeve, namely, Pereudesia, 
1920, is antedated by my Coptothyris, 1918 (replacing 
my Thomsonia, 1916, preoccupied). This fact has been 
pointed out in other papers. By the recognition of 
this form as a distinct genus there are now three 
finished types of northern genera in the Dallinine. 
J. Witrrip Jackson. 
Manchester Museum, 
May 21. 

The Ionising Potentials of Nitrogen and Hydrogen. 
Tn a paper published last autumn (Proc. Roy. Soc. 
A, 102, pp. 283-293, 1922) I suggested a new mode of 
attack on some ionisation problems and described its | 
application in experiments on mercury vapour.~ The 
object of the method is to give a direct means of 
studying the types of ion produced in a gas or vapour | 
by the impact of electrons of known speed. The 
experimental principle involved is the combination 
of an ordinary ionising potential arrangement with a 
simple positive-ray analysis apparatus. The exten- 
sion of the method to gases and some of the results 
obtained may be of interest. 
For the production of ions the common arrange- 
ment of a tungsten filament, a grid and a plate is 
used. Electrons from the filament are accelerated to 
the grid by a field V, and then retarded by an opposing 
field V, which also serves to draw positive ions 
toward the plate. A narrow slit in this lets through 
a beam of positive ions which are then further 
accelerated by a large electric field, V3. These ions 
are then bent in a semicircle by a magnetic field and 
detected electrically. Different values of V, bring 
ions of different m/e on to the detecting slit. By 
using two Langmuir pumps a sufficiently high vacuum 
is maintained in the positive ray box to prevent 
scattering, and very sharp peaks are obtained corre- 
sponding to different types of ion. 
In nitrogen it was found that for values of V, 
slightly above the ionising potential of 16:9 volts, only 
molecular ions of m/e =28 were present. As V, was 
increased small numbers of N** ions began to appear 
at 24:1+1°0 volts, while Nt ions were not present | 
in appreciable numbers until V, passed 27°7+1'0. 
These three critical potentials are interpreted as 
corresponding to the transitions N,—>N,++e, | 
N,—>Nt++N+2e> and N,—>2Nt+2e-. If this | 
interpretation is correct, the first ionising potential | 
of atomic nitrogen is about 11 volts and the second | 
NO. 2798, VOL. 111] 
NATURE. 

[June 16, 1923. : 
about 18 volts, assuming the heat of dissociation of 
nitrogen to be of the order of 140,000 calories, 
equivalent to six volts. 
At a value of V, corresponding to the K-limit for 
nitrogen (375 volts) the proportion of atomic ions 
increased very sharply. * 
Preliminary results on hydregen indicate that 
the ionisation of molecular hydrogen in the neigh- 
bourhood of 16°5 volts is not usually accompanied 
by dissociation as has been generally supposed. 
Whether there may be a small number of atomic ions 
produced at this point is not yet certain. Experi- 
ments are being continued. H. D. Smytn. 
Cavendish Laboratory, 
May 25. 

Chromosome Numbers in Aegilops. 
I HAVE recently been investigating the cytology 
of species of Aegilops, and find the chromosome 
numbers as follows :— 
Haploid 
Number, 
Aegilops cylindrica = 7 
A. ovata =I4 
A. ventricosa =14 
On morphological and other grounds I expressed 
the view in my monograph on “‘ The Wheat Plant ”’ 
that one or both of the former species appear to be 
involved in the ancestry of the vulgare group of wheats. 
Later I hope to discuss the significance of these 
chromosome numbers in relation to this hypothesis. 
JOHN PERCIVAL. 
University College, Reading, 
May 26. 

Effect of Insulin upon Blood Sugar Concentration. 
THE injection of insulin into rabbits causes the 
blood sugar concentration to be lowered, as deter- 
mined by micro methods. When a certain concen- 
tration is reached, 0°05 per cent. by Bang’s method, 
the animal goes into convulsions. If the animal is 
then killed and the sugar extracted from a large 
quantity of blood, it is found that it is without copper- 
reducing value as determined by the Wood -Ost 
method. This method is not lable to estimate 
substances in blood other than reducing sugars. 
There is, however, a considerable quantity of 
carbohydrate present, as indicated by the a-naphthol 
test. The substance is dextro-rotatory. We have 
not succeeded by acid hydrolysis in obtaining copper- 
reducing substances from it, though these can 
apparently be formed under certain conditions as a 
result of enzyme action in vitro. 
Dudley and Marrian (Proc. Physiol. Soc., May 19, 
1923) have shown that the glycogen content of the 
liver and muscles of animals is greatly diminished 
after insulin. We have obtained from the liver and 
muscles of rabbits after insulin a substance similar to 
that present in blood under this condition. Owing 
to its resistance to acid hydrolysis it would not be 
estimated by ordinary methods. The chemical 
nature of this sugar is being studied. 
We noticed in the case of some solid preparations 
that the a-naphthol reaction gradually disappeared 
on drying. Mr. H. F. Holden suggested that this 
might be due to polymerisation, and that on hydrolysis 
with acid the a-naphthol reaction would reappear. 
We find that this happens. It seems possible that 
the carbohydrate content of the animal body may be 
not appreciably diminished after large doses of 
insulin. The above facts would suggest that the 
sugar stored in the body as glycogen is converted 
