Document N2RaGgjg0zoYXE7REwJDx3oyE

-3- are without much practical importance, since in daily practice in industry the harmful effect is exercised more frequently by dusts mostly of mixed origin. Besides, what is most important is the physical and chemical constitution of the dusts and consequent ly their action on the system. Ill - WHAT ASH THE PHYSIOLOGICAL EFFECTS PRODUCED BY THE INHALATION OF DUST? - To be harmful from a respiratory viewpoint, dust must be of sufficient finess to pass through the nasal filters and be retained in the alveoli (minute air sacs)' of the lupgs. Particles found in autopsied lungs are of the order of one micron (a micron isl/lOOO of a millimeter or about 1/26,000 of an inch) or less in site - about the site of the comnon baoteria. Same dust particles found in lungs are as large as five or six microns although these sites are rather exceptional. There are five distinct types of reaction produced in man as the result of inhal ing dust. These reactions may be broadly classified, based on the primary cause, as followst (a) Those which result in lung fibrosis, commonly referred to as pneu moconiosis. These dusts contain free silica, asbestos, etc. How ever, it is not neoessary for fibrous tissue to be formed in order for the disease to be classed as "Pneumoooniosis". (b) Those which are toxic and are absorbed into the blood stream such as lead, cadmium, etc. (c) Those which result in what is commonly referred to as metal fume fever; such as sine oxide, etc. (d) Those which are allergic in character, such organio dusts as pollen, pulverised wood and flour, eto. The breathing of pulverised wood and flour is frequently associated with tuberoulosis. (e) Those commonly referred to as "nuisanoe dusts". These may cause ir ritation of the respiratory tract or passages and may cause con siderable discomfort, also headaohes of the dry "nasal" passage or sinus type and exposure to them may be associated with a high in cidence of respiratory illness. The rate and extent of these reactions are dependent upon the resistance of the indi vidual, the exposure period (concentration of particles .and length of exposure) tem perature and humidity of the air, rate of work, and the percentage of ingredients which are harmful. Owing to the length of time required to obtain a reaction by inhalation meth ods, the United States Bureau of Mines and the Public Health Service adopted about twelve years ago, a method of injecting small quantities of the dusts to be studied into the peritoneal cavity of guinea pigs. ("Response of Peritoneal Tissue of Dusts Introduced as Foreign Bodies" by Dr. John W, Miller, Dr. R.R. Sayers and Wm.?,Yant, Jour.Amer.Med.Assoc. Sept. 22,1934 - Vol*103,pps. 907-911). It was found that iden tical reactions ocour in eaoh animal injected with the same dust under the same con ditions and examined in the same time interval after injection. These reactions were essentially the same microsoopioally as that produced in the lungs and the gross ap pearance of the dust nodules was sufficiently differentiated to afford a means of classifying the physiological response to the dusts. There are three types of reaction: An absorption or dissolution of the dust. A proliferative reaction. An inert reaction. EK001493