[3] It is, of course, obvious that other circumstances besides overcrowding have to be reckoned with in considering these statistics. In the one-roomed houses the wages earned by the occupants must have been small, and the amount available for even the bare necessaries of life very limited, that, in fact, they were to be reckoned amongst the class defined by Mr. Rowntree as living in "primary poverty," whose earnings are insufficient to keep the body in a properly nourished condition. Mr. Rowntree has shown by statistics that the height, weight, and general condition of the poor are very much below those of the well-to-do labouring classes. Mention may also here be made of the investigations made by these gentlemen on the air of Board schools, which showed that in those buildings where mechanical ventilation was used the carbonic acid gas was three-fifths, the organic matter one-seventh, and the micro-organisms less than one-ninth of what was found in schools ventilated by the ordinary methods. In commenting upon this series of investigations, the authors write: "When we come to consider that the children who attend average Board schools for six hours a day are during that time subjected to an atmosphere containing on an average nearly nineteen volumes of carbonic acid per 10,000, and a very large proportion of organic matter, and no less than 155 micro-organisms at least per quart, we need not be surprised at the unhealthy appearance of very many of the children. It must also be borne in mind that many of them are exposed for nine hours more to an atmosphere which is about five times as impure as that of an ordinary bedroom in a middle-class house. They are thus breathing for at least fifteen hours out of the twenty-four a highly impure atmosphere. The effects of this are often intensified, as is well known, by insufficient food and clothing, both of which must render them less capable of resisting the impure air. The fact that these schools become, after a time, habitually infected by bacteria renders it probable that they also become permanent foci of infection for various diseases, and particularly, perhaps, for tubercular disease in its various forms." Further practical evidence of the manner in which the general death-rate for certain diseases is influenced by the conditions under which the poor are housed is afforded by statistics which have been collected at Glasgow. In the case of zymotic diseases, whereas the death-rate in tenements consisting of one or two rooms was 4·78 per 1,000, it fell to 2·46 in those of three or four rooms, and to 1·14 per 1,000 in those of five rooms and upwards. Again, in the case of acute diseases of the lungs, the death-rate was as high as 9·85 in the smallest tenements, and but 3·28 in the largest.