88 

contrary, a fairly highly susceptible animal. While 
without action on B. anthracis, dog serum, according to 
Petrie, has a powerful action on B. typhosus. Hektoen 
attributes some importance also to the leukins of the 
dog. Petrie, however, found none. 
The rat presents a more interesting problem, though 
it has to be remembered that there is no absolute 
immunity in this species. Behring, in 1888, showed 
that rat serum was anthracidal, while Metchnikoff found 
that the main defence was the phagocytic response. 
The thermostability of the bactericidal body in rat 
serum, as shown by Pirenne and Horton, is a most 
interesting feature. It acts equally well at 18° C. as 
at o° C., and remains active for fairly long periods in 
the cold. 
SUMMARY. 
To summarise, it must be confessed that the curiously 
contradictory and yet perhaps genuinely reasonable 
explanatory theses give us very little that is solid to 
grasp. No one example of normal immunity has yet 
been investigated as a complete problem. Partial 
mechanisms only have been studied. It might be con- 
cluded from the above that dogs are immune because 
dogs are dogs, and so for rats, fowls, and frogs, but 
that would not be quite the impression I should lke 
to make. Ifa certain animal is immune to a particular 
experimental infection, such as anthrax, one ought to 
be able to explain fully what local phenomena have 
occurred to prevent a general invasion by the organism. 
To do so effectively must involve the testing of each 
possible mechanism separately and in conjunction, and 
it must involve a return to the cytological study of 
the changes which the invading organism undergoes 
in situ. The problem must be attacked not only by 
methods which derive their authority from long ex- 
perience with the bactericidal properties of cells and 
fluids, but also by methods which reflect the trend of 
present-day studies on general metabolism both of 
parasite and host. With regard to the former much 
has been made of the capsule, but the data on the 
point are contradictory. In every set of experiments 
strict attention must be paid to the maintenance of 
virulence. It may, indeed, be found that by experi- 
mental selection a test organism which has once proved 
virulent for one individual of a resistant species may 
prove equally so for all individuals of the species. 
Strains of B. anthracis have been thus selected which 
are alleged to have killed fowls, rats, and frogs, but 
the experiments lack confirmation. 
NATURE 
[ JANUARY 20, 1923 
Another important aspect of the subject which has 
recently been brought to the forefront by Besredka 
relates to the site of inoculation of the test organism. 
In the course of his researches on the production of 
immunity by vaccinating that portion only of the 
body which is most susceptible, Besredka has turned 
his attention to anthrax infection in the guinea-pig, an 
animal notoriously difficult to protect by any method 
of vaccination. He shows experimentally what, by the 
way, had been amply demonstrated twenty years ago 
by Noetzel, that animals like the rabbit and guinea-pig 
can tolerate easily doses of virulent anthrax if introduced 
directly into the circulation or into the peritoneal cavity 
without contaminating the cutaneous tissues. This 
can be avoided by a special and careful technique. 
According to Besredka the skin of the guinea-pig is 
the only susceptible portion of the guinea-pig’s anatomy, 
and if it had no skin it would be a highly refractory 
animal instead of being, as it is, one of the most sus- 
ceptible. He further demonstrated the possibility of 
securing solid immunity to anthrax, by whatever 
route inoculated, by vaccination of the skin with 
the attenuated Pasteurian vaccines. I do not wholly 
accept much of the evidence adduced so far in support 
of the conception of partial or local immunities or 
susceptibilities, but I believe the matter is worth the 
fullest investigation. In any case it is obvious that 
future work on natural resistance must take count of 
the possibility of very diverse immunities or suscepti- 
bilities apparently combined in one immune whole. 
I have dealt with species resistance solely, but it 
has to be remembered that there are racial variations 
of resistance within the species. For this reason the 
study of the mechanism of normal immunity will doubt- 
less demand the services of the geneticist, who will be 
responsible for securing pedigreed stock for experimental 
purposes. This is no fanciful suggestion. In connexion 
with these most promising developments in experimental 
epidemiology which are being carried out in this country 
and in America the services of the geneticist must be 
invaluable. The dietetic factor, too, may prove of 
supreme importance in experiments on natural resist- 
ance, and there is already a body of evidence pointing 
in this direction. It is possible also that we may learn 
from comparative observations on the rationale of 
natural immunity in plants to fungal infections. In a 
recent address by Blackman some of these mechanisms 
reveal extraordinarily interesting relationships between 
the attacking fungus and the cells of the immune 
host. 

Helium in the United States. 
By Dr. Ricuarp B. Moore, Chief Chemist, U.S. Bureau of Mines. 
(Pe of the projects started in the United States 
during the war and since continued, is the 
extraction of helium from natural gas for use in balloons 
and dirigibles. In 1907, Cady and McFarland published 
a report on the presence of helium in a number of 
natural gases, mainly from Kansas, U.S.A. Some of 
the samples tested ran as high as r} per cent. helium 
by volume, although the majority of them were con- 
siderably below this figure. 
Early in 1915 the present writer received a letter 
NO.12777 VOL. 111] 
from Sir William Ramsay, written under date of 
February 28. In that letter it was stated that the 
British Government was interested in new sources of 
helium other than the atmosphere, in the hope that a 
sufficient amount could be obtained for use in dirigibles. 
It was only during my recent visit to England last 
summer that I learned of Sir Richard Threlfall’s 
intimate connexion with the origin of this demand for 
a supply of helium by the British Government. 
American Government officials heard no more of the 

