. 
FEBRUARY 15, 1917] 
NATURE 
479 
PaRALLAXES OF PRocyON AND ALTaIR.—Among the | could readily contaminate by the nose or mouth the 
large number of stellar parallaxes recently determined 
by photographic methods at the Leander McCormick 
Observatory, Dr. S. A. Mitchell has directed special 
attention to the results for Procyon and Altair (Pop. 
Ast, vol. xxv., p. 38). For Procyon, the values which 
have been previously determined are remarkably con- 
sistent, ranging from 0-287” to 0-34”, and Dr, Mitchell’s 
parallax of 0-309’+0-007" is in perfect agreement with 
the mean of all. The parallax arrived at for Altair is 
0-218"+0-007", and this again accords very closely 
with the weighted mean value 0-220” derived from 
earlier determinations, 
DENSITIES OF VisuAL Binary Stars.—An interesting 
attempt to advance our knowledge of the densities 
of stars of different classes has been made by E. Opik, 
of Moscow, in a discussion of the probable densities 
of visual binaries for which orbits have been calcu- 
lated (Astrophysical Journal, xliv., p. 292). He pro- 
ceeds by developing a series of formule by which 
the density can be determined when the surface 
brightnesses of the components are known. The 
surface brightness itself is determined from the spec- 
tral type, in conjunction with the corresponding effec- 
tive temperatures given by Wilsing and Scheiner, 
and an application of the radiation formula of Planck. 
The mass-ratio of the two components must also be 
known, and where such data are not available, ap- 
proximate values are estimated from the differences 
in magnitude. The densities calculated in this way 
for forty pairs cover a wide range (0-012 to 5:9, in 
terms of the sun), but aconsiderable proportion of them 
approach the density of the sun, The mean values 
for the different spectral classes, which are only to 
be regarded as roughly approximate, are as follows :— 
Spectral type No. of stars Density 
Ao-A5 aes fat 9 0-65 
Fo-F8 te hs 19 0°59 
G SFr se se 7 0:23 
BS ¥e oe 5 0-072 
So far as they go, though the author does not com- 
ment upon this point, the figures show an order of 
density opposite to that which would be expected on 
the supposition that celestial evolution is along a line 
of descending temperature only. When accurate 
magnitudes and spectral types (or coldur-indices) be- 
come available for each component, it will be possible 
to obtain separately the densities of the components, 
and an important region of stellar statistics will be 
opened up. 
EXPERIMENTS ON ASCARIS INFECTION 
IN HONG KONG. 
A* important paper by Capt. F. H. Stewart, Indian 
Medical Service, appeared in the British Medical 
Journal for July 1, giving the life-history of Ascaris 
lumbricoides, which is extremely common both in man 
and the pig at Hong Kong, where the author is 
stationed with the 74th Punjabis. In this preliminary 
communication he showed that the parasite presents 
an alternation of hosts. Thus, when ripe eggs reach 
the alimentary canal of the rat or mouse the larve 
are liberated, and six days after infection they are 
found in the blood-vessels of the lungs and liver, and 
the host is seriously ill with pneumonia. They next 
pass from the blood-vessels into the air-vesicles of the 
lung, causing hemorrhage into them. On the tenth 
day they occur only in the vesicles and in the bronchi. 
If the disease does not prove fatal, the host recovers 
on the eleventh or twelfth day, whilst on the sixteenth 
day it is free from parasites. The affected animals 
NO. 2468, VOL. 98] 
food of man or the dust and earth of his surroundings. 
Capt. Stewart has continued his experiments since 
the foregoing date both with A. lumbricoides and 
A, suilla, and finds that the larvae appear in the 
bronchi, trachea, and mouth of the rat and mouse on 
the night of the seventh day and during the eighth 
day after infection by the mouth, and he believes that 
they pass by means of the saliva on to the food which 
is being nibbled by the rodents. It is possible that 
one attack of Ascariasis in rats renders them immune 
against subsequent attacks, but further confirmation. 
is necessary. He found that the larve survived 
longest (twenty-four hours) in blood on moist bread. 
In water, normal salt-solution, and in mouse’s blood 
they survived three hours. : 
Out of five experiments to test the infection of pigs. 
from the foregoing rodents, three gave positive re- 
sults, two negative. In estimating the value of the 
negative experiments the very high mortality among 
the parasites employed under somewhat unnatural con- 
ditions must be kept in mind, Capt. Stewart en- 
deavoured to obtain an estimate of this mortality by 
comparing the number of ripe eggs given to a mouse 
with the number of larve found in the lung. An 
average dose contained about 5000 eggs, whilst the 
number of larve found in the lungs did not exceed 
fifty. The transfer from the rodent to the pig is 
probably the most vulnerable part of the life-cycle, 
since the larva is a very delicate organism. The 
author also carried out control experiments with the 
pig. 
Lastly, Capt. Stewart carried out some experiments 
which demonstrated that A. marginata of the dog has 
-also its intermediate host in the mouse. 
He concludes by stating that if ripe eggs of A. 
lumbricoides are swallowed by rats or mice they hatch. 
The larvz bore into the venules of the portal system 
or ascend the bile-duct. They are found in the dilated 
capillaries of the liver between the second and the 
fifth days. As their diameter is three times that of a 
blood-corpuscle in the mouse, they cannot pass through 
a normal capillary. The liver-cells in the neighbour- 
hood of the larvz undergo rapid degeneration, and the 
larve are thus enabled to pass by the hepatic vein 
and vena cava to the heart, and by the pulmonary 
artery to the lungs, where they are filtered off at the 
entrance to the capillary field. Embolism of the 
arterioles takes place, and the larve pass with the 
effused blood into the air-vesicles on the sixth day. 
They are found in the bronchi on the seventh day, 
and in the trachea and mouth on the eighth day, after 
infection. The larve from the lungs of rodents can 
infect the pig, and it is probable that in Nature infec- 
tion of both man and the pig takes place by food) 
contaminated by rats and mice. W. C. M. 
SEX-LIMITED FACTORS IN HEREDITY. 
PEW of the results obtained in recent years by 
students of heredity on Mendelian lines have 
appealed to biologists as a whole more forcibly than 
such cases of “ sex-limited"’ inheritance as are exempli- 
fied by colour-blindness in mankind or the special type 
of wing-marking in the magpie-moth (Abraxas grossu- 
lariata) described by Dr. Leonard Doncaster in his 
work on the ‘Determination of Sex.” Those who 
have followed the progress of research on the subject 
during the last five years recognise how important 
have been the results obtained by Prof. T. H. Morgan 
and his colleagues in their studies of inheritance in 
fruit-flies of the genus Drosophila. 
An admirable summary of these studies, entitled 
