870 
Supplement to the ^'Tropical ArjticuUuHst*' 
[June 1, 1904, 
a blood parasite, but the carrier of the infection 
has not been discovered. It is inoculable by the 
injection of a small quantity of blood from an 
infected sheep, and I am glad to say that a method 
of inoculation has been discovered which is both 
safe and simple. 
The disease of the horse which I formerly 
described as Biliarj' fever is also due to a blood 
parasite of the malarial type, and is doubtless 
carried and communicated by a tick or some biting 
insect, such as a mosquito. The evidence is also 
accumulating that the dreaded horse-sickness is 
also communicated by a biting flying insect, sucli 
as a mosquito, but no organism has as yet been 
discovered in the blood. It is true that Dr. Eding- 
ton has reported that he has discovered a malarial 
parasite in the blood of some cases of horse-sickness, 
but at present the general opinion is that these 
cases had been complicated with equine malaria 
or "Biliary fever." A tick has been conviced of 
being the carrier of the blood-parasite which causes 
that very fatal form of malignant malarial fever 
of our domestic friend the dog, and Mr. Lounsbury 
has shown tiiat this new disease of cattle which 
Dr. Koch has called " African Coast Fever" is also 
communicated by a tick. There is as yet some 
doubt whether more than one species of tick car- 
ries and-communicatea the organism of this last 
and most dreaded plauge. Dr. Koch is of opinion 
that the common blue tick is also a transmitter of 
the organism of this disease. If the blue tick alone 
were the only carrier of the parasite, it would be 
much easier to check the spread of the disease, as 
like ordinary red- water, it could only be spread by 
cattle. It will be much more difficult to control, 
however, if the infected ticks can be carried by 
other animals than cattle. At the present time, 
the duty of this Colony is to use every endeavour 
to keep the disease out of our territory as long as 
possible, in the hope that we may be able to obtain 
a clearer knowledge of the nature of the disease, 
and how it is spread, and we may also at the same 
time acquire some practical experience of the 
value of the present method of inoculation discov- 
ered by Dr. Koch. 
It is of interest to mention that the principal 
measures which the Transvaal and Nalal Colonies 
ore taking for arresting the spread of this disease 
are fencing and dipping. I strongly recommend 
the farmers of the Cape Colony to copy this 
example. I would also like to add that at the 
intercolonial Veterinary Conference which was 
held recently at Bloemfontein a motion was unani- 
mously carried recommending the respective 
Governments of the Biitish S.A. Colonies to take 
into serious consideration, the practicability of 
completely eradicating the ticks which affect farm 
stock from the country. 1 commend that resolu- 
tion also to your consideration. 
BACTEKIA AND THE KITROGEN PROBLEM- 
By Geoegb T. Mooee, 
Physiologist, Bureau of Plant Industry, U.S.A. 
{Concluded from page 95.) 
In the meantime there is still one other means 
at hand which can be used and has been used for 
countless centuries as a most efficient method of 
Conserving the world's nitrogen supply. Ever 
since the time of Pliny and other early writers 
upon agricultural topics, it has been known that 
certain leguminous crop?, such as clover, beans, 
peas, etc., did not require the same amount of 
fertilizer as other plants, and indeed it seemed as 
though they actually benefited the soil instead of 
being a detriment. Various theories have been 
advanced to account for this effect, perhaps the 
most widespread opinion being that members of this 
family, owing to the unusual length and strength 
of their root system, were able to draw upon a 
store of food that was not available to wheat and 
corn and other crops not belonging to the pod- 
bearing group. It is only within a comparatively 
recent time that the real cause of the beneficial 
effect of these legumes has been fully understood, 
and it seems that here again the bacteria are respon- 
sible for the nitrogen-gathering power ; for it is 
because these plants are able to fix and use the free 
nitrogen of the air that they are of such benefit in 
rotation and in reviving poor and exhausted land. 
The immense yields of wheat following alfalfa or 
clover are easily understood when it is realized 
that there has actually been added to the soil a 
certain definite amount of nitrogen in such form 
that the wheat can be benefited by it. Such effi- 
cient users of the atmo.spheric nitrogen are clover 
and peas and similar crops that they can actually 
live and thrive in a soil that lias not the first trace 
of combined nitrogen within it. If quartz sand be 
ignited to red heat, thus burning out all the nitrates, 
and then be planted with peas or beans, it is 
possible to bring these plants to full maturity 
without in any way allowing a particle of fixed 
nitrogen to find its way into the soil. Oa the other 
hand, wheat or potatoes, or crops not legume^, 
will die as soon as the small amount of nitrogen 
available from the seed is exhausted. What is the 
reason for this ? It can not be merely a difference 
in the length or extent of the root system, because 
plants flourish where it is certain there are no 
available nitrates whatever. For a long time the 
presence of certain peculiar nodules or tubercles 
upou the legumes has been noted and speculated 
upon. These formations are always present upon 
th3 roots of leguminous plants grown under pro- 
per conditions, and may vary in size from that of 
the smallest pin head, in some clovers, to a cluster 
as large as a pptato. They have been thought to 
be due to the bites of worms or insects, or to be 
caused by conditions of the soil and various abnor- 
mal climatic effects, and only within very recent 
years has it been learned that these formations 
are due to the presence of innumerable bacteria, 
and that unless these tubercle-producing bacteria 
exist the plant is no more able to use the nitrogen 
from the air than wheat or any of the other crops 
which do not have such nodules on their roots. 
Just where the nitrogen is fixed and how it is 
used by the plant have been debated questions. Some 
have supposed that the presence of the bacteria in 
the roots simply acted as a stimulus, and that the 
leaves of the plant were thus able to take in nitro- 
gen as a gas and to elaborate nitrates from it in 
some such way as carbon is formed from carbon 
dioxide, It seems much more probable, however j 
