=Remedial Measures.=—Means have been taken to diminish the prevalence of the above dust diseases, in several cases with remarkable success. In the case of steel-grinding, for instance, the mortality is greatest with dry grinding, and least with =wet grinding=. Wet processes have been applied to others of the industries named, with a like success. Where the dust cannot be avoided, the use of =steam or electric fans=, to deflect the dust away from the workman, has been found successful; and in many cases, =free ventilation= of the workshops has greatly diminished the mortality. Where none of the above measures suffice, the use of =respirators= ought to be insisted on. Breathing through the nostrils ought to be carefully maintained, as thus the dust is to a large extent stopped before reaching the lungs. The dangers of lead poisoning may be avoided by absolute =cleanliness=, the hands being always washed before taking meals, and the nail-brush used to secure complete cleanliness beneath the nails. 2. =Living Substances.=—The pollen of plants in some persons produces a distressing form of disease, called =hay-asthma=, which is apt to recur each year, and is sometimes only curable by living in a town or removing to the sea-coast. The amount of pollen floating about in the atmosphere is considerable; 95 per cent. of it is grass-pollen, and this form and the pollen from pine-trees appear to be the most powerful in inducing hay-asthma. According to some authorities, hay-asthma is rather due to the minute particles constituting the scent of various flowers, than to the pollen; but that is probably not the usual mode of origin of the disease, though it may be in some cases. In some cases, true asthma results from smelling particular plants. Here as in the case of hay-asthma a peculiar idiosyncrasy is involved, only a very small proportion of those exposed to the minute particles suffering from asthma. The spores of many fungi and of other living organisms are constantly being floated about in the air, until they find a suitable resting place, when they settle and proceed to grow and multiply. The souring of milk, the fermentation of a saccharine solution, the moulding of bread, the presence of mildew, the blighting of corn, and numerous other phenomena are due to the growth of organisms carried by the atmosphere from one part to another. 3. =The Contagia= (microbes or germs) of the acute infectious diseases are minute living organisms, known as bacteria. Hence these diseases may be carried about by currents of air, some much more easily than others. Some of the contagia have a persistent vitality. Thus the contagia of scarlet fever, diphtheria, or small-pox may infect a room for months, causing the disease in question, when infected articles in the room are disturbed. The contagia of typhus fever and of measles, on the other hand, are short-lived, and do not usually resist free ventilation and exposure to sunlight.