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his soda water contained 15,700 per c.c. A fifth maker's soda water contained 12,400 organisms per c.c.
and that of a sixth maker, who used an inefficient filter and admitted that he washed his bottles in well
water, contained 25,600 per c.c. An examination which was made of the aerated water manufactured
at the East Surrey regimental soda water factory brought to light a fact of some interest. It was
found that the original water contained only 11 organisms per c.c., and that this water was actually
boiled before use, a procedure which Hankin, after examining the water, looked upon as being quite
on a par with endeavouring "to paint the lily." Nevertheless the soda water made at this factory
contained 4,800 microbes per c.c. Hankin found explanation of this apparent anomaly in the fact that
the water employed for washing the bottles contained after use 26,400 organisms per c.c.; it was
derived from a suspected well, but the high degree of impurity was no doubt mainly due to "dirt,
perspiration, etc., from the hands and clothes of the coolies" who conducted the washing operations.
Hankin's conclusions differ in some important respects from those already quoted; thus, he states
that" the gas in the soda water acts as a poison to the microbe, so that a bottle which was teeming
with bacteria when first used is generally perfectly free from them at the end of a week." He finds,
as did Slater, that "the cholera microbe appears to be the easiest to kill," and adds "the typhoid
microbe is unfortunately among the most resistant to the action of carbonic acid." Again, he states
that " soda water in India, owing to the high temperature, has to be bottled at a much higher pressure
than in England (180 lbs. as against 30 or 40 lbs per square inch), and it is probable that in the
Indian soda water the gas acts on the microbe at this higher temperature, and pressure greatly aids its
action." He goes on to contrast the results obtained by him in the case of a particular organism (bacillus
liquefaciens fluorescens)with those obtained in England by Slater. In India the organism, even after
36 hours' stay in aerated water, was enfeebled and lost the power of producing green colouring matter,
whereas Slater found it living and uninjured more than 5 weeks after bottling. Hankin says "I
venture to conclude that the gas at relatively low pressure in English soda water is a less powerful
germicide than that present in Indian soda water. However this may be, it is clear that any risk of
infection from bad soda water can be avoided if it is kept a week or more before use."
It will be seen that Hankin seems to have found the samples examined, more than a week after
bottling, sterile, and that he attributes important germicidal influence to the pressure factor. These
facts are not in agreement with the results referred to as having been obtained in temperate climates.
G. Malfitano (Giornale della Reale Societa Italiana d'Igiene, Milano, 1897, xix, 545-551) found, as the
result of experiments which he made, that some germs were killed by exposure for 60 hours to a
pressure of 50-60 atmospheres, but that, even under these conditions, complete sterilisation was not
produced.
Illness attributed to the consumption of aerated water.
The two diseases which must be regarded as water-borne par excellence are cholera and enteric
fever. No instance of communication of cholera by aerated water appears to have been noted, although
in India, where cholera is specially prevalent, aerated waters are largely consumed. The speedy
destruction of Koch's spirillum in water charged with carbonic acid gas may possibly account for this.
Ginger-beer* has, in one or two instances, been suspected of causing spread of enteric fever, and Hochstetter
refers to an outbreak of the same disease at Mainz in 1894, which was attributed to contaminated
aerated water. Having regard to the large quantities of aerated water consumed in this country, it might
perhaps have been anticipated that if enteric fever were ever actually spread by this means, the fact
would have been by this time rendered sufficiently apparent. It needs to be borne in mind, however,
even assuming it possible for aerated water to be potent for mischief, that the fact of a number of
sufferers from the disease having all consumed the same aerated water is less likely to be established,
than would be the fact, say, of there being a common drinking water or milk supply in the case of
those attacked. Again, the bacteriological finding is to the effect that the bacillus typhosus cannot
live long in water charged with carbonic acid. Hankin appears to consider the water safe 7 days
after bottling. Slater is only satisfied with an interval of 14 days, and even then stipulates that
the water must originally have been obtained from a good source. The observations of the latter
observer regarding the increase in the number of organisms when the water is kept, after escape of the
gas, and his conclusion that the bacteria "are not in all cases killed, but have their development
arrested," need also to be borne in mind. The possibility of other forms of disease (gastro-intestinal
disturbance, diarrhoea, etc.) being caused by the consumption of aerated water, prepared from impure
water or to which impurity has obtained access in the process of manufacture, is not an altogether
remote one. In the existing state of knowledge no great reliance can be placed upon the disinfecting
action of carbonic acid, and even if the water has been bottled a considerable time, there is
no certainty that among the more resistant forms of organisms which survive, there may not be
pathogenic germs.
A special source of risk in the case of aerated water is that, at some stage in the process of
manufacture, the water may have taken up metallic impurity. This question seems to have engaged
a good deal of the attention of manufacturers. It is stated in an article "On mineral water machinery
and metallic contamination" (Lancet, January 7,1893), that ordinary water containing excess of carbonic
acid is capable of taking up into solution distinct quantities of lead, copper and zinc, but not tin.
Dr. Slater, in referring to risk of lead-poisoning, says this source of danger has "been practically
eliminated by the use of block-tin pipes, thickly-tinned cylinders, and syphon heads consisting of almost
pure tin, or protected by porcelain linings or electro-plating." In occasional instances metallic
impurity has been detected in aerated waters, and though apparently, at the present time, most of
* See the Milroy Lectures, 1902. Dr. Corfield refers to an inquiry made by Dr. Parsons concerning a special incidence
of the disease upon young adult males employed at an ironworks. "The beverage commonly in use by such persons was gingerbeer,
made often at home from the water of polluted wells, and not wholly boiled."