530 . 
Journal of Agricultural Research 
Vol. XXX, No. 6 
inches of the tube, being deposited 
in a thin film on its inner wall. When 
smut spores were used the tube was 
quickly coated with a black layer, 
the darkest zone being situated near 
the inlet, showing that they were 
precipitated very promptly upon enter¬ 
ing the charged field. When the 
apparatus was suitably adjusted very 
few spores passed through the tube. 
This was determined by passing the 
outgoing air through a wash bottle 
•containing oil and water and ex¬ 
amining the fluid microscopically. 
Only occasional spores were found. 
Preliminary steps were then taken 
toward developing an electrical pre¬ 
cipitation apparatus which might be 
operated satisfactorily under orchard 
conditions. However, pressure of 
work, expense of the electrical equip¬ 
ment necessary, and the fact that very 
satisfactory results were being ob¬ 
tained by the method described below 
led to the discontinuance of exper¬ 
iments with the electrical method. 
The writers believe, however, that 
this method has possibilities of adap¬ 
tation to problems involving a study 
of the spore-content of air. The re¬ 
sults obtained appear to be in gen¬ 
eral agreement with those of Buller 
(p. 192-195) 5 , who has studied the 
electrical charges on spores from a 
different point of view. 
FILTRATION ON MEMBRANES 6 
Early in the consideration of the 
problem it occurred to the writers that 
it might be possible to devise an appa¬ 
ratus which might be run continuously 
and so constructed that spores could be 
filtered from the air upon transparent 
or translucent membranes on which 
they might be counted under the 
microscope. Preliminary tests with 
membranes prepared from cloth, fiber, 
gelatin, nitrated cellulose, cellulose ace¬ 
tate, and viscose were unsuccessful. 
The three latter-named materials were 
not sufficiently porous to allow ade¬ 
quate passage of air. Pure filter paper 
was tried, and it was found that, by 
specially treating 7 soft Swedish filter 
paper, nearly pure cellulose, there was 
produced a tough, waterproof mem¬ 
brane which proved to be satisfactory. 
Some special Swedish filter papers and 
Whatman's hardened filter paper were 
then investigated and found to be suf¬ 
ficiently waterproof to resist disinte¬ 
gration when wet by rain. The paper, 
however, should not be so altered by 
treatment with acid that it loses its 
porosity and precludes adequate passage 
of air. 
A motor-driven vacuum pump was 
then set up and a heavy-walled rubber 
tube was used to connect its intake with 
a special apparatus for holding the filter 
paper (fig. 1). It consisted of a thick- 
walled brass tube (A) on the machined 
end (B) of which was screwed a very 
closely fitting brass cap (C) in the 
middle of which was an aperture 1 inch 
in diameter. A disc (D) of filter paper 
of suitable diameter, underlain by a 
supporting disk of fine silk fabric of 
similar size, was placed upon the ma¬ 
chined end of the metal tube, and the 
cap screwed tightly over it. In this 
way it was held firmly in position, the 
cap making a joint that was air-tight, 
while a circular area 1 inch in diameter 
was exposed for purposes of filtration. 
A perforated rubber stopper (E) con¬ 
nected the device with the suction 
tube by means of a glass tube. Numer¬ 
ous tests of the capacity of the machine 
with different filters of the type used 
throughout the experiments showed 
that approximately 1,200 liters of air 
passed through the apparatus in an 
hour. 
The membranes were removed at 
intervals as circumstances warranted. 
As soon as a membrane was removed it 
was placed in a small Esmarck dish and 
treated with a small amount of glycerine 
to make sure that the spores remained 
in place. In each test a membrane sim¬ 
ilar to the one used for filtration was 
placed beside the latter, collected with 
it, and studied microscopically, as a 
control against chance accumulation of 
air-borne ascospores. Studies of these, 
however, showed so few spores that it 
seemed unnecessary to make any cor¬ 
rection in the results for them. The 
number of spores caught on the mem¬ 
brane was determined by direct counts 
under the microscope. The olivaceous 
color and characteristic form and size 
of the spores made them easily observed 
without staining. If the number was 
5 Buller, A. H. R. researches on fungi, v. 1 , illus. London, New York, etc. 1909. 
6 In later studies the junior author and his coworkers have developed another filtration technique which 
is being used in their further work. Orchard air is drawn by means of a motor-driven suction apparatus 
through a suitably arranged filter of nitrocellulose. Thence it passes through a gas meter which records 
the volume. At the end of the run, the nitrocullulose filter, bearing the spores caught, is dissolved in a 
suitable glass container in a mixture of alcohol and ether and allowed to evaporate to a gel. The asco¬ 
spores settle to the bottom and their number is computed on the basis of microscopic counts. This is an 
adaptation of a technique developed by Pasteur. It will be described in more detail in a later paper. 
7 The filter paper was dipped for about one-half minute in nitric acid, sp. gr. 1.42, transferred for a 
brief period to sulphuric acid (equal volumes of 1.84 sp. gr. sulphuric acid and water), and washed in 
water and then in a weak solution of ammonia. 
