496 
Great improvements have been made in the 
effectiveness of the absorbent materials used 
in the canisters, and this, in turn, has in- 
ereased several fold the general efficiency 
which it was possible to attain at the time 
when the manufacture of the masks was first 
undertaken, and hence to diminish the amount 
of material to be placed in the canisters. The 
significance of this will be understood when it 
is realized that there is a considerable friction 
to overcome when the inhaled air is drawn 
through the canister. This was so great in 
the earlier masks, that it made necessary a 
suction on the part of the wearer of the mask 
equal to that required to raise a column of 
water in a tube to a height of six inches; an 
effort not incomparable with that made by 
many asthmatic sufferers to draw air into the 
lungs. This frictional resistance has been 
materially-lessened by the improvement in the 
protective materials, and every reduction, 
however slight, is a great boon to the troops. 
The materials used in the canisters are se- 
leeted to react with gases of an acid character, 
and with those capable of destruction by oxi- 
dation, a process like that generally known as 
combustion. Much reliance is, however, placed 
upon the absorptive power toward gases ex- 
hibited by many porous substances, notably, 
high grades of charcoal. The principle is the 
same as that utilized in the “charcoal filters” 
sometimes attached to our faucets to clarify 
water supplies. 
Of late a new problem has been presented, 
because of the use of gases in the form of 
“smoke-clouds,” which easily pass through 
the protective materials contained in the can- 
isters. This has necessitated the addition of 
another filtering medium, and has necessarily 
added somewhat to the resistance to be over- 
come. 
How serious this “ neutralization ” of troops 
through the continuous wearing of masks may 
be, is illustrated by the condition which ob- 
tained before one of the recent violent at- 
tacks on the Western Front. It has been 
stated that the enemy fired gas-shells (mainly 
mustard-gas) at the rate of two hundred thou- 
” SCIENCE 
[N. 8. Vou. XLVIII. No. 1246 
sand shells per day for four days, each shell 
probably averaging about five pounds of ma- 
terial. While: the gas-masks will protect the 
wearer from the inhalation of this gas, they 
must have required one or more renewals 
during this period. This attack was followed 
by a smoke-cloud attack which necessitated 
the use of the extension filters, thus subject- 
ing the troops to added labor in breathing, 
after days of constant use of the mask. The 
physical strain under such conditions can not 
fail to have been severe. It is not, however, 
to be supposed that the enemy was allowed to 
spend his time in full comfort. 
As a means of detecting the approach of a 
toxic gas, canaries and white mice are placed 
in the trenches, as they are peculiarly sensi- 
tive to these chemicals and show signs of dis- 
tress from dilutions which are unnoticed by 
man, especially when the gases are nearly 
odorless. 
Of the offensive side of this gas-war it is 
obvious that little can properly be made pub- 
lic. There is reason to believe that our Amer- 
can chemists are making valuable contribu- 
tions in this field—Henry P. Talbot in the 
Atlantic Monthly. 
SCIENTIFIC BOOKS 
Agricultural Bacteriology. By W. H. Conn. 
Third edition, revised by Haroxp Jorn 
Conn. Philadelphia, P. Blakiston’s Son & 
Company. 1918. Pp. x-+ 357. Illustrated. 
with 63 figures. $2.00. © ; 
The first part of the book is taken up with 
a discussion of the general characters of mi- 
eroorganisms and their réle in the decompo- 
sition of organic matter. The second part, 
which occupies practically one fourth of the 
volume, is devoted to the relations of bacteria 
to soil fertility. The cycles of carbon and 
nitrogen are presented. This section includes 
a chapter on ‘The Manure Heap and Sewage” 
and on one “Bacteria in Water.” In the 
latter the réle of water in the distribution of 
disease-producing organisms is discussed. The 
third part presents the relation of bacteria to 
milk and to butter and cheese. 
