1026 Transactions of the American Institute. 



leaf, the rot is fatal unless the affected part is removed. There is no 

 spontaneous suspension. So in numberless instances in plants and 

 animals. We are told these germs are in the breath and in the 

 secretions, in the mouth, etc. This is unquestionably true, and a 

 very strong argument that they were not the cause of tlie disease of 

 which they are an attendant. They go in and out, and come out as 

 they went in, unaffecting and unaffected. 



Some of the properties are very evident. It is heavier than the 

 atmosphere. It is generally within a few feet of the ground. Seldom 

 rising above thirty or forty feet when the surface is level. We have 

 often found it in the yards and lower stories of buildings, but not in 

 the upper stories. It is often discoverable on hill sides when the 

 wind blows from a malarious district. It is probably not a gas, but 

 consisting of excessively minute particles ; it rises into the air by the 

 mechanical action of watery vapor. It seems, however, to form an 

 atmosphere of its own, as it obeys the laws of diffusion. This it 

 might do even if it were not a gas. 



4th. The means by which nature destroys malaria. — Ozone, vege- 

 tation and running water, are the agents nature employs in purifying 

 the air. What we call ozone is simply an active state of oxygen. 

 It is always in the atmosphere when the air is pure. It is produced 

 "by the sun's rays on water and volatile oils and by electrical cur- 

 rents. It burns up all putrid and malarious emanations. It is the 

 great scavenger of the atmosphere. We have constructed an instru- 

 ment for determining the presence of ozone. It is the same as that 

 for detecting malaria. Instead of putting a permangate solution iit 

 the bulb, put in a solution of starch with a few grains of iodide of 

 potassium dissolved in it. 



This is, in effect, Schonbein's test. He directs the employment of 

 papers smeared with the solution. These papers have never been 

 satisftvctory in ray hands. The mode indicated above is perfectly 

 determinate and satisfactory. By having a standard solution of the 

 starch compound a perfect determination is attained. The volume 

 of air that passes through the bulk is, of course, exactly equal to the 

 water that runs out, so that if a gallon of air in one place produces 

 the same effect as two gallons in another, the relative intensity is, of 

 course, determined. The instrument for malaria and one for ozone 

 gives the operator the means of determining at once tlie presence or 

 absence of these agents. If one is present we need not look for the 

 other, as they cannot exist coincideutly. If ozone is present malaria 



