Dr. A. Jacobi in a paper read before the Congress of American Physicians and Surgeons at Washington as early as 1894, sums up as follows:

"I may be finally permitted to add the oral testimony of more than a dozen European medical men and dozens of Americans. Every one was asked by me: What do you know of the production of a specific germ disease out of, or through, sewer air? The uniform answer was: There is a general vague impression among the public, but I never saw a case or could prove one.

Some of the conclusions to be drawn from this paper would be as follows:

The atmosphere contains some specific disease germs, both living and dead.

They are frequently found in places which were infected with specific disease.

In sewer air fewer such germs have been found than in the air of houses and school rooms.

Moist surfaces - that is, the contents of cesspools and sewers, and the walls of sewers - while emitting odors do not give off specific germs even in a moderate current of wind.

Splashing of the sewer contents may separate some germs, and then the air of the sewer may become temporarily infected, but the germ will sink to the ground again.

Choking of the sewer, introduction of hot factory refuse, leaky house drains and absence of traps may be the causes of sewer air ascending or forced back into the houses. But the occurrence of this complication of circumstances is certain to be rare.

Whatever rises from the sewer under these circumstances is offensive and irritating. A number of ailments, inclusive, perhaps, of sore throats, may originate from these causes. But no specific diseases will be generated by them except in the rarest of conditions, for specific germs are destroyed by the process of putrefaction in the sewers, and the worse the odor the less the danger, particularly from diphtheria.

The causes of the latter disease are very numerous, and the search for the origin of an individual case is often unsuccessful.

Irritation of the throat and naso-pharynx is a frequent source of local catarrh; this creates a resting place for diphtheria germs, which are ubiquitous during an epidemic, and thus an opportunity for diphtheria is furnished.

Of the specific germs, those of typhoid and dysentery appear to be the least subject to destruction by cesspools and sewers. These diseases appear to be sometimes referable to direct exhalation from privies and cesspools. Very few cases, if any, are attributable to sewer air.

A single outlet from a sewer would be dangerous to general health because of the density of odors (not germs) arising therefrom. Therefore a very thorough and multiple ventilation is required.*

The impossibility or great improbability of specific diseases rising from sewers into our houses, protected as they are, or ought to be, by good drains and efficient traps, must, however, not lull our citizens and authorities into indolence and carelessness.

For the general health is suffering from chemical exhalations, and the vitality of cell life and the powers of resistance are undermined by them."

Naegeli experimented by enclosing putrescent and putres-cible liquids in sealed vessels together for over three years without air infection taking place, and by drawing air through sand wetted with putrescing liquid and then through sterile infusion without infecting the latter.

Sir Edward Frankland of England found that "the moderate agitation of a liquid does not cause the suspension of liquid particles capable of transport by the circumambient air," but that "the breaking of minute gas bubbles on the surface of a liquid consequent upon the generation of gas within the body of the liquid is a potent cause" of such suspension, and that therefore the stagnation of sewage or constructive defects in sewers may form cesspools of putrefaction in the sewers and generate gases which may form these bubbles. Such defects in sewer construction are totally unnecessary, and cesspool accumulations should, as I have said, never be allowed.

In 1883 P- Miquel* published the results of his experiments on the comparison between sewer and street air in •"The Sidewalk Ventilators in New York City are almost all obstructed."

*"Les Organismes Vivants de 1'Atmosphere," Paris.

Paris, and from 1893 to 1899 he made periodical tests which were given in the following table: bacteria in country air, city air, and sewer air, per cubic meter.

Country Air.

City Street.

Year.

Montsouris.

Hotel de Ville.

Sewer Air.

1893.............

285

8,435

5,015

1894.............

230

9775

2,920

1895.............

330

7,615

2,590

1896.............

.......

6,205

3,965

1897.............

197

5410

3,875

1898.............

...........

5,200

2,075

1899.............

........

6,595

2,910

Uffelmann experimented with a house drain in 1886-7, taking nine samples at intervals during a year. He found an average of 3 bacteria per liter of sewer air. Petri found 1 bacterium and 3 molds in 100 liters of air in a Berlin sewer on one occasion and no bacteria and 1 mold on another.

Carnelley and Haldane* made important studies on sewer air in England in 1887. They found less bacteria in the sewers than in the streets in almost all cases, averaging 9 per liter in the former and 16 in the latter. They concluded that "The micro-organisms in sewer air come entirely, or nearly so, from the outside, and are not derived, or only in relatively small numbers, from the sewer itself." They found a considerable increase, however, under violent splashing. They found less bacteria in the air in contact with quietly flowing sewage rather than more, on account of the wet surface.

Robertson** found less bacteria in the air of the sewers of Penrith than in the street air, averaging 4 to 6 respectively. More bacilli were found in the former and more cocci in the latter.

*T. Carnelley and J. S. Haldane. "The Air of Sewers, proceedings of the Royal Society of London, 1887, XLII, pp 394 and 501.

**"A Study of Micro-Organisms in Air. Especially Those in Sewer Air, and a New Method of Demonstrating Them. British Med. Journal, Dec. 15, 1888.

Laws found that even splashing in sewers was unlikely to produce appreciable infection, and that sewage falling into an egg-shaped sewer, 11 ft. x 9, from the middle of its height, produced practically no effect on the number of germs.