APRIL 7, I 923] 
manures do not. This difference we are now engaged 
in exploring. 
The same method of procedure is used as in study- 
ing the effects of artificial fertilisers. A full scientific 
investigation into the causes is carried out, but simul- 
taneously an attempt is made to find some working 
solution of the farmers’ problems. The shortage of 
farmyard manure is still as acute as ever, and to keep 
more animals with the view of making more is un- 
economic. At Rothamsted we have attempted to 
produce farmyard manure from straw artificially and 
without animals. This has been done by Mr. E. H. 
Richards and Dr. Hutchison by simulating the essen- 
tials of the natural process, namely, watering straw 
with a salt of ammonia (actually ammonium sulphate, 
but calcium carbonate is mixed with the straw), and 
leaving the heap so that the air can get in and the 
organisms can do their work. The product is not 
yet equal to the natural substance, but it is steadily 
_ being improved, and the very serious difficulties are 
gradually disappearing in Mr. Richards’s competent 
hands. Five years ago a few ounces only of this 
artificial farmyard manure had been prepared ; last 
year several thousand tons were made on various 
farms in different parts of the country, and the news 
is spreading. The serious problem of developing the 
work from the laboratory to the farm scale has been 
possible through the generous and _public-spirited 
action of Lord Elveden, There seems here the possi- 
bility of aid to the farmer and of the development of 
an important new industry. 
Meanwhile a full scientific investigation is being 
carried on to discover wherein farmyard manure differs 
from artificials. One important difference is already 
known and is being investigated by Dr. Keen. Farm- 
yard manure opens out the soil particles leaving bigger 
_ pore spaces ; it allows of the retention of more moisture 
and the better circulation of air. All these effects are 
_ beneficial. 
There is also another difference. Farmyard manure 
and also plant residues (which are substantially the 
same thing) decompose in the soil, giving rise to many 
substances of different types. The plant foods are 
among the end products: indeed, in natural condi- 
tions, and, to a large extent, in farms and gardens 
also, it is in this way that plants obtain their food. 
In using artificial manures we supply these end pro- 
ducts at once instead of waiting for them to be liberated 
gradually by the natural decomposition. Further, 
we do not by any means know the whole of the pro- 
cesses whereby plant food is made. But there are 
certain intermediate products, and it is quite possible 
that some of these may have a special effect on the 
growing plant. Curious stimulating effects are pro- 
duced by substances formed when soil is steamed, 
or when oxidation is accelerated by addition of char- 
coal, and we have obtained the same results with small 
quantities of picric acid ; such bodies might well be 
formed as intermediates in the decomposition of farm- 
yard manure. The whole effect suggests an action 
like that of the vitamins of plant physiologists or the 
auximones of the late Prof. Bottomley. The chemical 
department at Rothamsted, under Mr. Page, is follow- 
ing out the process, and the botanical department 
No. 2788, VOL. 111] 
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NATURE 
something or contains something which artificial | under Dr. Winifred Brenchley, will test any inter- 

469 
mediate products which may be obtained. 
A further important factor, which probably governs 
the whole situation, is that a great part of the process 
of decomposition and plant food production appears 
to be brought about by living organisms in the soil. 
Simultaneously, therefore, with the chemical and 
botanical investigations, the various biological depart- 
ments are busily engaged in studying the organisms 
that are doing the work. 
It is a wonderful story that is being revealed. The 
soil is shown to be the abode of a vast population of 
living organisms of the most varied kind. Some of 
them are remarkably small; among them one which 
brings about the last stage in the formation of nitrates 
—an organism which Rothamsted just missed forty 
years ago: another, also just missed at Rothamsted, 
which has the remarkable property of fixing nitrogen 
in the nodule of the clover plant. Others are larger 
and more easily picked out, but their exact place in 
the soil economy is not easy to determine: probably 
they are concerned in the preliminary stages of the 
decomposition. 
It is impossible to peer into the soil with a micro- 
scope, so that indirect methods of exploration have 
to beused. At Rothamsted the organisms are counted 
and the work they do is estimated by some chemical 
process : virtually we take a census of population and 
production in the soil. Like other census methods, 
it is comparative only: a single census is not much 
use ; it is not until several have been taken that one 
can find how the numbers and activities of the popula- 
tion are being affected by various conditions. The 
census is therefore repeated periodically and the 
results plotted on curves from which it is possible 
to deduce the effect of various factors on the particular 
organisms counted. 
These curves brought out the remarkable result 
that partial sterilisation increased bacterial activity, 
and investigation showed that the normal virgin soil 
must contain other organisms besides bacteria—organ- 
isms, moreover, which .were detrimental to bacteria 
and tended to keep their numbers down. A search 
for such organisms showed that protozoa were present : 
many forms have since been found in the soil, some 
of which are known to feed on bacteria. Mr. Cutler 
has discovered how to count them, and with the co- 
operation of willing workers has succeeded in carrying 
out perhaps the most remarkable census yet made 
of the bacterial and protozoan population of a natural 
field soil. Before the census began many months 
were spent in perfecting the methods and technique, 
and in making preliminary studies of the soil. The 
details were carefully arranged with the statistical 
department, and it was decided to take the census 
many times at short intervals. Time to a bacillus 
or a protozoan is a different thing from what it is to 
us, and instead of taking the census every ten years, 
or even every ten days, it was taken daily, and at the 
same hour every day. Many repetitions were needed 
so that the statistician might feel safe in drawing 
conclusions from the data. The census was therefore 
made every day for 365 consecutive days, and no less 
than seventeen different organisms were enumerated. 
A team of five workers kept the investigation going 
