In the days when open fireplaces were almost the only means of heating houses they were of great value in aiding ventilation. Nowadays our stoves, radiators and furnaces do not help us in this matter, and we must take additional pains to see that ventilation is provided in some other way. Of course the simplest and most perfect method is to permit the free passage of the wind through open doors and windows. Every room should have its air thus completely renewed at least once a day. The mere renewal is done in a few minutes, but a longer time is required to dislodge the organic vapors and other impurities that lurk in the corners and behind furniture. In schools and work shops this should be done during the intervals for meals, and in churches between services. But in our climate it is not possible to have windows and doors open during all the time a room is occupied, except in very warm weather. It is seldom, however, that the window of a bedroom cannot be opened for a few inches all night without direct benefit to the occupant of the room. His bed, of course, must not be immediately in the draught. Curved pipes, ventilating shafts and slides under the windows are substitutes easy to use when windows cannot be actually opened. GUARD YOUR WATER SUPPLY Water supplies differ greatly in purity and composition, and are of the utmost importance in their effect upon the general health of a household. There is nothing which requires to be guarded more carefully. Absolutely pure water is almost unknown. Rain water collected in open countries is the purest, though even it takes up matters in its passage through the air, and in towns may be strongly acid. All waters which have been in contact with the soil dissolve out of it numerous inorganic and organic substances. Waters are described as hard or soft, hardness being the popular expression for the property of not easily forming a lather with soap. It is due to the presence of salts of lime and magnesia. Hard waters, if their hardness be not excessive, are agreeable and wholesome for drinking, but not well adapted for laundry or bathing purposes. They tend to harden vegetables cooked in them, and do not make as good tea as soft water. Rain water is, of course, the softest, but as a rule lakes yield waters also quite soft. When a good and wholesome water cannot be obtained from springs or rivers, as in malarial districts, and when there is reasonable ground for thinking the ordinary sources are contaminated by epidemics, it is well to fall back on the rainfall for drinking purposes, with special care that it is collected in a cleanly manner.