ADDRESS. 23 



isolation of infectious disease, and to the disinfection (by superheated steam) 

 of materials which have been in contact with the sufferer. 



These microbes, whether friendly or hostile, are all capable of multi- 

 plying at an enormous rate under favourable conditions. They are found 

 in the air, in water, in the soil ; but, fortunately, the presence of one species 

 appears to be detrimental to other species, and sunshine, or even light 

 from the sky, is prejudicial to most of them. Our bodies, when in health, 

 appear to be furnished with special means of resisting attacks, and, so 

 far as regards their influence in causing disease, the success of the attack 

 of a pathogenic organism upon an individual depends, as a rule, in part 

 at least, upon the power of resistance of the individual. 



But notwithstanding our knowledge of the danger arising from a 

 state of low health in individuals, and of the universal prevalence of 

 these micro-organisms, how careless we are in guarding the health 

 conditions of everyday life ! We have ascertained that pathogenic 

 organisms pervade the air. Why, therefore, do we allow our meat, 

 our fish, our vegetables, our easily contaminated milk, to be exposed 

 to their inroads, often in the foulest localities ? We have ascertained 

 that they pervade the water we drink, yet we allow foul water from our 

 dwellings, our pigsties, our farmyards, to pass into ditches without 

 previous clarification, whence it flows into our streams and pollutes our 

 rivers. We know the conditions of occupation which foster ill-health. 

 Why, whilst we remove outside sources of impure air, do we permit the 

 occupation of foul and unhealthy dwellings 1 



The study of bacteriology has shown us that although some of these 

 organisms may be the accompaniments of disease, yet we owe it to the 

 operation of others that the refuse caused by the cessation of aniinal and 

 vegetable life is reconverted into food for fresh generations of plants and 

 animals. 



These considerations have foi'med a point of meeting where the 

 biologist, the chemist, the physicist, and the statistician unite with the 

 sanitary engineer in the application of the science of preventive medicine. 



Engineering. 



Seicage Purification. 



The early reports to the Association show that the laws of hydro- 

 statics, hydrodynamics, and hydraulics necessary to the supply and removal 

 of water through pipes and conduits had long been investigated by the 

 mathematician. But the modern sanitary engineer has been driven by 

 the needs of an increasing population to call in the chemist and the 

 biologist to help him to provide pure water and pure air. 



The purification and the utilisation of sewage occupied the attention of 

 the British Association as early as 1864, and between 1869 and 187G a 

 committee of the Association made a series of valuable reports on the 

 subject. The direct application of sewage to land, though efiective as a 



