=Rebreathed Air as a Poison.=--The following extracts are taken from an article by Dr. John Hartley, in the Lancet: "The fresh-air treatment of consumption" appears to be made up of three essential factors: (1) the discontinuance of the supply of bacilli from without; (2) the supply of an abundance of nutritive material to the tissues; and (3) the supply of an abundance of fresh air uncontaminated by the products of respiration. This seems to mean that the tissues, if not too enfeebled, may be trusted to deal with the bacilli already present if their metabolism is kept going at high pressure. Fresh air is now the "official" remedy in the treatment of tubercle. Why is it so ignored in the case of other diseases? Has the pneumonic or bronchitic no need of special ventilation because his microbe is of a different breed? The air was intended not only for phthisical patients or patients suffering from pneumonia but for _all_--diseased and healthy alike--and it is still the natural medium in which the poisonous products of tissue metabolism excreted by the lungs are further broken down and rendered harmless. Dr. A. Ransome has done great service not only by his onslaught on "air sewage" but also by his coinage of the term; for a thoroughly good opprobrious epithet resembles a good wall-poster in its power of arresting and enchaining the attention of the many. It was long ago pointed out that certain constituents of expired air are intensely powerful nerve poisons. These considerations should surely make us look on rebreathed air and sewer gas, not as mere carriers of accidental poisons, such as influenza and pneumonia and the like, but as _poisons per se_, and I wish to be allowed to record a few very imperfect observations made by myself during some years past chiefly on the subject of rebreathed air, with certain inferences which I think tend, however feebly and imperfectly, to show that the poisons we expire have _per se_ very definite effects on tissue metabolism and need not a mere perfunctory admixture with fresh air but very large and very continuous dilution before they are rendered innocuous--that is to say, innocuous to _all_; for while some persons appear to be almost immune, others seem intensely susceptible. The first observation I will allude to was made in the autumn of 1896, in cool weather. I had to take a long night journey by rail after a long and hard day's work. The train was full and the compartment I entered was close; so, as I was tired and fagged, I sat in the corridor by an open window, well rugged up, throughout the journey. The compartment was completely shut off from the corridor by a glass door and windows, through which I could freely inspect its occupants. Two remarkably fresh-complexioned, wholesome-looking young fellows got into the compartment at York. They formed a remarkable contrast to the pallid and fagged-looking travelers already there. The windows and