requires pipes or channels to allow it to flow into or out of reservoirs. With most persons air seems to be an abstract idea rather than a substance of vital consequence to the whole living creation.

I have stated in the paper that air, which has once passed through the lungs is unfit to be respired again, just as unfit as any other substance which has once passed through the system is to be used, as it were, over again. So that, were there no other source of contamination to the air of a building, ventilation would be rendered necessary by the very presence of living beings. As it is, however, there are so many other evil influences at work in most houses and other buildings that the necessity is made far more absolute.

It is usually only in times of panic, caused by the approach or presence of some fearful epidemic, or of a calamity such as last year threatened this nation, that people seriously turn their attention to sanitary matters and at times like these they accept the wildest schemes and act upon the crudest notions until, finding matters are no better, and perhaps rather worse than before, and the fright beginning to wear off, they relapse into carelessness, and vote sanitary science all nonsense. think defective education is responsible for a great deal of this. I do not intend to assert that the generality of people, at any rate in the upper and middle classes, are what is commonly called ignorant, probably most of those who would be willing to turn their attention to sanitary matters, not being professionally engaged in them, have had at least the usual amount of education, as the term is commonly understood. The three R's are familiar to them as are also mathematics, Greek, and Latin, and they can probably converse in one or more of the modern languages, but what may be called the science of living, i.e., how life is sustained, and the reasons why sanitary matters should be so carefully attended to in order that health and strength may be ensured, are things of which comparatively few know anything at all.

In this paper I wish to impress upon the reader the very great importance of pure air to the human body, and to shew how such air, or as pure as the district affords, may be ensured in our houses.

It has been stated before, that one of the elements of the atmosphere unites in our bodies with certain of the elements composing the food we eat. This union of elements is a true combustion, though a slow one, as true and real as the combustion of coals in a fire grate.

Our food, having been decomposed in the body, is brought into a state proper for sustaining life and animal heat in us

when, as venous blood, it is submitted to the purifying action of oxygen brought into the body by the lungs. Without the element, oxygen, which I have before stated forms part of the atmosphere, this purification could never take place, for the other gases have no power of the kind. It will be obvious upon consideration that if a portion of oxygen in the air we have breathed has united with elements composing our food, that portion is removed from the atmosphere and must be replaced if breathing is to be continued.

I will here explain for the benefit of persons who may be wholly unacquainted with chemistry, what is meant by the term "element." The ancients held that there were four elements, or simple bodies, viz., earth, air, fire and water, but the progress of chemical knowledge soon revealed the fact that these were not elementary bodies at all, three of them being compound, while the fourth, fire, may be more properly described as a condition of matter. An element is a body which cannot, as far as we know, be divided or decomposed. It is unalterable and indestructible, and is therefore called a simple body or element.

Elements, however, combine with one another, and lose their individuality, so to speak, in the compound. Thus two simple bodies, gases, hydrogen, and oxygen, unite in certain definite proportions and form water; but the water can be again decomposed into its constituents.

Air, although I have called it a compound, is not, chemically speaking, strictly so; it is a mixture of gases which preserve their individuality as sand and sugar would do if they were mixed in a vessel.

We are at present acquainted with more than sixty elements or simple bodies.

But to return to the atmosphere. It must not be imagined that we remove all the oxygen from the air we breathe, on the contrary, the removal of a small per centage renders air incapable of supporting life, and a still less diminution causes the difference between fresh air and vitiated.

I have said a good deal about the effect which the act of breathing has upon the atmosphere, because I want to make very clear the fact that the same air should not be respired more than once, and that it cannnot be so, even in part, without danger to health. The other results of respiration, viz., carbonic acid and water have been mentioned before, and it was shown that they contributed to foul the air.

I think we may, without serious error, divide noxious gases into two classes, placing those which are negatively poisonous in one class, and those which are positively, or actively, so in the other. To the former belong-as types-carbonic acid and

nitrogen, both of which, though not in themselves injurious, are incapable of supporting life; so that an atmosphere composed wholly of these gases, or containing them in undue proportion, is fatal, from its negative qualities, to living beings. Carbonic acid gas, as before explained, is one of the products of combustion and respiration, while nitrogen forms seventy-nine per cent. of the volume of the atmosphere. Its negative qualities are there, however, counterbalanced by the presence of oxygen.

With gases of the second class the case is very different. Some of them-such, for instance, as sulphuretted hydrogen and carbonic oxide-are fearfully active poisons. The former exists in putrid eggs, and some other animal and vegetable matters; also in certain waters, called hepatic, such as those of Harrogate. It is usually formed in the putrefaction of vegetable and animal matters; hence it is found in sewers, and especially in cesspools and similar places where accumulations of filth take place. During the emptying of such receptacles, workmen sometimes suffer from asphyxia, or, as the French call it, "le plomb" (probably from the oppression on the chest which accompanies it). Parent Duchatelet states that the symptoms of poisoning by sulphuretted hydrogen are very alarming, for "the individual is either seized suddenly, and dies instanly, or, if the quantity of deleterious gas is too little to bring instant death, the asphyxiated person, suddenly losing consciousness, is taken with convulsive movements or other very grave nervous disturbances, and it is only after several days that he recovers perfect health." The presence of sulphuretted hydrogen is readily detected by its odour, which resembles that of rotten eggs, but it is soothing in its nature if inhaled, which renders it especially dangerous when escaping into rooms where persons are sleeping.

It will be seen, then, of what extreme importance is the prevention of the passage of sewer gases into our houses, and I have entered somewhat fully into the properties of these foul gases, because I wish to show clearly that they are not things to be trifled with.

Carbonic oxide is like carbonic acid, a product of the combustion of carbon, or the union of carbon with oxygen, but the proportion of oxygen is less in the former than in the latter compound. Carbonic oxide, though a dangerous gas, need not be considered at length here, as it does not, I believe, exist in sewers, and is very seldom found in houses. It cannot, like sulphuretted hydrogen, be detected by its smell, as it is inodorus as well as colourless and tasteless. Carbonic oxide burns with a blue flame, which probably most people have noticed at some

time or other, either playing over burning charcoal or dancing upon an ignited lime kiln.

I must now leave this part of the subject and say a few words useful, I hope, to those who are about to choose a house, whether as tenants or purchasers, and in doing so I may, perhaps, travel somewhat away from ventilation.

The first consideration, after settling which town or part of the country it is desired to live in, should be the situation of the house, i.e., not only its aspect, but the condition of the soil on which it stands, and its position with regard to any ponds, streams, rivers, or other natural features.

Taking first the aspect. It is generally considered that a house is most favourably situated when its principal front is towards the south-east, for it then gets the morning sun, while the rooms are sheltered to a great extent from the midday heat. The south-west is the rainy quarter in the country, and should, therefore, be avoided. A gravel soil is commonly to be preferred to any other, although, I believe, that in towns which are well sewered and drained, the nature of the soil is not of so much importance; indeed, one might readily imagine a case in which a gravel soil would be anything but a benefit-as, for instance, where there is a pond near the house, and on about the same level, or in towns where precolating cesspools are the fashion. Running water near a house is not objectionable, indeed, many persons consider it rather beneficial than otherwise; but, before taking the house, care should be exercised in ascertaining that the water is free from sewage contamination, especially if it be a small stream, or liable to dry up in summer. Stagnant ponds should always be avoided, especially if the house is on nearly the same level.

With regard to artificial sanitary conditions, as distinguished from natural situation, soil, ect., the first question to be asked of the landlord should be as to a good water supply to the house other than from wells on the premises. There being no such supply, nor means of laying one on, would certainly be against the house, inasmuch as where there are no water works, there is generally no system of sewerage, and it may safely be said that in any unsewered town, there is hardly a well, the water of which is fit to drink; to say nothing of the labour of pumping water into cisterns, etc. From this follows, naturally, the question as to the sewerage of the town or village. If there is no system of sewers, I would say, “live anywhere else if you possibly can," for the absence of sewerage indicates the existence of some form of cesspool, an evil so great that nothing but absolute necessity should cause any person to take a house to which a cesspool is attached. I say "some form of cesspool," for I am

quite aware that there are schemes which profess to do away with water closets, and cesspools, and partially with sewers, but upon examination, they will all be found wanting in some material point. Among these plans are the "dry earth" and "pail" systems, both, in my opinion, but forms of cesspools. If the town or village is sewered, the first point is to make sure that the house drains are properly connected with the sewers. It is no uncommon thing for the drain to be carried from the house to the outside of the sewer, and to stop then, being thus rather worse than useless. The bricklayer would probably call this "leaving another job." After seeing that the connection is properly made, i.e., that the pipe really passess into the sewer, the next thing to be done is to find out of what the house-drain is made, or how it is laid. These points I have alluded to before, and shall therefore pass them over here (See page 15). Next, make sure that the house drains are properly ventilated. The landlord or builder will probably tell you that they are "trapped" and that on foul gas can pass the trap. This is a great delusion, and should not be listened to for a moment. The trap is a very useful and necessary thing, but it must not be expected to do more than it can, and, in order to make this clear, I will explain what the common syphon trap is, viz., a bent pipe generally of

NOTE--The common trap has not the ventilating pipe B.

the form shewn in section in the sketch. These pipes always retain a certain quantity of water (indicated by shading in the figure) when in use, in the dip or bend. It will be observed that the upper part of the pipe dips into the water which completely fills the bend, and the water is sometimes said to "seal" the trap and it is assumed that it will entirely prevent any gases from passing into the house. A little consideration will shew, however, that if the gas is generated in such quantities as to cause any considerable pressure in the sewers it will readily pass through the water into the house. That this has actually happened, the following incident recorded by Dr. Carpenter will shew. The ventilating pipe spoken of was in fact doing duty as a water-pipe from the cistern! "On the night of October 17th I was aroused by a loud noise proceeding from the closet; it continued at intervals throughout the next day. Unable at first to account for it, I eventually found that it was caused by the ventilating pipe doing duty as water-pipe to the overflowing cistern (during a very heavy rainfall). There was no room for exit of foul air from the sewer, which, therefore, was forced through the trap of the water-closet, with, at times, the force of steam through the