The Origin of the Nitrates in Griqualand West 125 
of soil and refuse from several cliffs, and carried out the necessary ex- 
periments after my return to town. 
A quantity of coarse sea-sand was washed with acids and water, 
dried, ignited, mixed with 1 per cent. of chalk, and distributed into six 
porcelain basins. After the basins and their contents had been 
sterilized, they were placed under separate bell-jars, together with a 
little basin of sterilized water, in order to provide the necessary 
moisture. Three of them were devoted to series A, and three to series 
B, of the experiment. 
In series A each basin received 5 ccm. of a solution of sulphate of 
ammonia,* just enough to moisten the sand. The first basin received 
nothing else ; to the second was added 1 ccm. of a decoction of a little 
soil from one of the caves ; and to the third one ccm. of a liquid obtained 
by shaking a sample of such soil with some sterilized water. 
In series B the first and third basins received 5 ccm. of a decoction 
of feeces of rock rabbits, and the second one a liquid obtained from the 
same material by cold maceration only. The first received nothing 
else, but the third basin an addition of a few drops of the liquid used 
for the second dish. 
I need hardly add that all instruments used for these operations had 
been sterilized beforehand, and that each experiment was made in 
duplicate. The six bell-jars were placed in a room with closed shutters, 
and kept for twenty days. 
On analyzing the contents of the six basins, I found the following 
results : 
Series A. 
1. No trace of nitrate. 
2. No trace of nitrate. 
3. Nitrate present, corresponding to 0:0008 nitrogen. 
Series B. 
4, No increase of nitrate. 
5. Considerable increase of nitrate, corresponding to 0:0015 nitrogen 
from 0°0003. 
6. Same as No. 5. 
These results show that no nitrate was formed in the sterilized 
materials, but that it was formed in the unsterilized animal matter, and 
in the basins to which a little fresh substance had been added. 
In order to ascertain the presence or absence of microbes in the 
different samples of sand by direct observation, I took a little of each, 
shook it with sterilized water, mixed 1 ccm. of each sample of water 
* Ammonium sulphate and potassium sulphate each one gramme dissolved in one 
litre of distilled water and sterilized. 
