J. McG. Smith (Sixth Annual Report of the Metropolitan Board of Water Supply and Sewerage, 1893) found as an average of 20 tests 225 germs per liter in the sewers of Sydney, the particular forms being without exception organisms common in street air.
In 1894 Dr. A. C. Abbott of Philadelphia found germs were transported on a current having a velocity of 16.5 cm. per minute, but not by one of 8.6 per minute or less. Dr. Abbott's conclusions were that the danger of bacteria being transmitted under natural conditions was practically negligible.
Dr. Charles Harrington* says "The majority and the best of German investigators, such as Flugge, Rubner, Gartner, Soyka, Prausnitz, and others maintain that sewer air and sewer gases are quite incapable of conveying the germs of typhoid fever and other infective diseases. It is true that some of the gases given off in the putrefaction processes, which go on in sewers are more or less poisonous, but whether they are capable of producing any injurious defects depends very much on the amount inhaled and on the degree of concentration. In any event they are certainly incapable of producing any infective disease in the absence of the specific germ."
Mr. Allen Hazen writes that Col. Ruttan has "investigated the plumbing in a considerable series of houses in Winnepeg with the general result of finding that plumbing is not associated with typhoid fever. In fact his statistics show a somewhat larger proportion of cases of typhoid fever in the houses where the plumbing is good, than in those places where it is defective."
•A Manual of Practical Hygiene, Phila. and N. Y., 1901.
Mr. Hazen sums up the best current American opinion in the following sentence "After many years of experience and long continued investigation there is not the slightest reason to believe that infectious diseases are carried by the air of sewers."*
G. C. Whipple** says "Typhoid germs do not readily leave a moist surface. Sticky by nature they adhere until desiccation loosens their dead cells. For this reason sewer air is not to be looked upon as a direct means of infection."
In 1907 Major W. H. Horrocks* of the Royal Army Medical Corps of Great Britain in some analyses of sewer air at Gibraltar found under certain conditions germs carried from the sewage into the air. His principal deduction from these tests was stated as follows: "Specific bacteria present in sewage may be ejected into the air of ventilation pipes, inspection chambers, drains and sewers by (a) the bursting of bubbles at the surface of the sewage, (b) the separation of dried particles from the walls of pipes, chambers, and sewers, and probably by (c) the ejection of minute droplets from flowing sewage."
This paper created some excitement among sanitarians in the world, and caused many to return almost to the old time terror of "sewer gas."
But closer examination of the experiments of Horrocks and of his summary of conclusions does not appear to justify any such alarm. These conclusions as stated by himself' were only such as had practically been admitted by previous investigators we have already quoted.
*Engineering News, LIII, 246.
••In the latest American Text Book on Typhoid Fever (Typhoid Fever, New York, 1908).
•Proceedings of the Royal Society, Series B, Vol. LXXIX, No. £ 631, p. 265. Feb. 7, 1907.
In some of his experiments Major Horrocks used strongly foaming soapy solutions and vigorous splashing resulting in the ejection of a few germs (B. prodigiosus) from the sewage in the same way with other investigators. In another case he obtained a few germs from quietly flowing sewage. But this again had been observed by others and ascribed to the drying of sewage on the sides of the pipes, or from the transmission through it of fine bubbles caused by decomposition or chemical action in the sewage. Certain germs are known to dart rapidly through the fluids in which they exist under the action of flagella, celia or whips attached to their bodies. Others have a slow serpentine, spiral or creeping motion and it might, at first thought, seem possible for the swiftly darting kinds to leap out of the water like a flying fish and thus escape into the air. A flying fish can leap from the water and remain a few moments in the air. But the germ has not the peculiar muscular, flexible, and springy body, fins and tail of the flying fish. The long flagella of the germ presents precisely the construction which would prevent aerial flight especially when heavy with water soaking. Cuttle and jelly fishes more nearly resemble the flagellated bacteria and these do not fly about in the air. To expect such action on the part of even the swiftest darting germ would be as reasonable as to expect to see a devilfish paddle himself with his long tentacles up to the surface of the ocean and soar away above the clouds. Mariners have not as yet recorded having seen this feat and microscopists are as little likely to have to tell the tale about disease germs. That germs do not progress by their own motive power through air was indicated by Pasteur when he proved that it was not necessary to insist upon hermetic sealing or cotton fiters to keep them from gaining access to a flask of infusion. It is now well known that if the neck of the flask be drawn out into a long tube and turned downwards, and then a little upwards, even though the end be left open, no contamination will gain access. The force of gravity will prevent them from ascending the long arm of the tube into the neck of the flask and impregnating the infusion.
Moreover Major Horrock's bacterium prodigiosus has a very slow and sluggish motion. His conclusion that germs may probably escape from minute droplets ejected from flowing sewage seems perfectly natural and requires no special explanation.
A repetition of Major Horrock's experiments by another well known bacteriologist* recorded in the following table showed similar results, and in this case also the germs ejected were so few as to be, from a sanitary point of view, considering the great volume of the air into which they were transmitted, entirely negligible, as he showed in various ways and from the following table.