882 Mockeridge. — So me Conditions influencing the Fixation of 
In connexion with the question of aeration, some experiments were 
started to obtain some idea of the extent of the superiority of the sand- 
slope method over that of ordinary liquid cultures as regards the yield 
of nitrogen per unit of carbohydrate used. Two series of six flasks each 
were employed, the first series, numbering from i to 6, containing Bottom - 
ley’s solution, and the second, numbering from 7 to 12, being supplied with 
Ashby’s solution. 50 c.c. of 1 per cent, solution were put into each flask, 
and 50 grm. of sand to form a slope were added to Nos. 4, 5, 6, 10, 11, and 
12. The process of inoculation was carried out in exactly the same manner 
as before, with the suspension of Azotobacter in sterile water, and Nos. 3 , 4, 
7, and 10 were sterilized in the autoclave to act as controls, after which all 
were incubated at 28° C. for seven days. At the end of this period the 
contents of each vessel were transferred to a Kjeldahl flask and analysed 
for its nitrogen content, the results being as follows : — 
Table V. 
Culture Solution. 
With or 
without 
Sand. 
Nitrogen 
Content. 
1. 
Bottomley’s solution — sterile . . . 
Without 
0-41 mg. 
2. 
, , with Azotobacter 
» 
1.38 mg. 
3* 
1.52 mg. 
4- 
„ sterile . . . 
With 
0*41 mg. 
5- 
„ with Azotobacter 
>5 
5-67 mg. 
6. 
„ ,, 
>> 
5.95 mg. 
7- 
Ashby’s solution — sterile .... 
Without 
0-41 mg. 
8. 
„ with Azotobacter . . 
0-69 mg. 
9- 
>> 9 > 
? > 
0-69 mg. 
10. 
„ sterile .... 
With 
055 mg. 
11. 
,, with Azotobacter . . 
99 
4-39 m g- 
12. 
u )> 
79 
4.12 mg. 
Gain in 
Nitrogen. 
Gain in Average 
Nitrogen Gain in 
on 1 grm. Nitrogen , 
0.97 mg. i-94 m g. 
1. 1 1 mg. 2.22 mg. 
2.08 mg. 
5.26 mg. 10-52 mg. 
5.54 mg. 1 1.08 mg. 
io-8o mg. 
0-28 mg. 
0.28 mg. 
0-56 mg. J 
0.56 mg. ) 
0.56 mg. 
3.84 mg. 
3-57 mg. 
7.68 mg. ) 
704 mg. \ 
7-41 mg. 
The effect of the increased aeration due to the sand slope is made very 
clear by these figures, and the difference between the simple liquid culture, 
and that on a sand slope, in rapidity of growth was equally apparent to the 
eye. On the sand slopes, the gelatinous growth appeared earlier, grew 
more rapidly, and darkened much more quickly than did that on the 
liquid. On the sand-slope cultures in Bottomley’s solution, the film of 
Azotobacter appeared over the whole surface on the third day ; its formation 
was deferred until the fifth day in the sand-slope cultures in Ashby’s 
medium and in the ordinary cultures without sand in Bottomley’s solution, 
while in Ashby’s liquid cultures no perceptible growth occurred, and the 
fixation of nitrogen, as shown in the above table, was very slight. The 
effect on the rapidity of growth of the increased aeration due to the sand 
was very strikingly shown at the same time by some cultures grown on 
ethyl alcohol. When an ordinary liquid medium was inoculated, growth 
took place very slowly, the film appearing over the surface only after the 
