Document 3e64RLwL44rwEdEBKy2evB5N3

Octoher 24, 1939 Mr. 1. 0. Carlisle, President, Toledo Vitrified Brick Company, 1220 lUdieon Avwnue, Toledo, Ohio. Dear Mr. Carlislei I have your lotter of October 17 end vlll try to aeke clear vbat the present position with regard to dust pertloles is. It has been proved that particles of duot that gain entrance into the lung must be not larger than 10 microns in else and all duct counts that are aede by the Public Health Service, the United States Bureau of Mines, ths Saranac Laboratory, tha Harvard School of Public Health, and ourselves are based on s total count of particles under 10 alcroas. It is true that mot of tbesa particles will be around 3 microns in muny industrial dust exposures. Thsrs is some dispute as to what may be the action, if any, of particles of ultra-microsoopic else but this does not have much practical importance. Our clinical observations are based upon many types of exposure for which the 10 million particle count is a foot rule. It is not by any naans a measure* ment of precision but it is an index that is very useful both in enabling tha investigator to nave an adequate conception of the actual silica batard in a given place} also it forms a useful means of checking the value of dust exhaust equipment or other dust control measures that may be eat up. With respect to free silica, that is silica existing in a free or uacomhlned state, it is the accepted opinion anong tna investigators in this country, England, South Africa, and Canada, that only free alilea oausas silicosis, and that com bined silica, such as magnesium silicate, sodium silicate, or any other chemical combination, does not cause the disease. As far as wa know, only one silicate dust, namely asbestos, has been shown to produce a typical characteristic flbbosls of the lungs whioh ws call asbsstosls. Asbmatosis pathologically is quits dif ferent from silicosis and can bs differentiated from it either by X-ray or by mlcrosooplo examination of pathological specimens. Generally speaking, * duot is dangerous in proportion to ths amount of free ailloa which it oontalna. Another fmotor, however, enters into this pioturs. It has been shown that where certain substances may be present in the dust along with the silica, these substances may tend to affect the motion of the silica in ths lungs, slther retarding it or aooelaratlng it. Both metallic aluminum and aluminum oxide, for insteaoc, art credited (at laast on tha basis of animal sxparimsntatlon) with being able to inhibit ths motion of silica entirely, febstaaoss present! In ths dust of Iron or* mines and in some granite works apparentlyretard ths eotioa of fliloe. At lesst this is the only sxplsnstion which can bs offered for ths feat that la these certain industries, siiioosls develops much mors slosly then * Mr. Cjlisle- 2 be expected if the aili-.a content of the dust were the only governing factor. On the other hand, a owe of the Britiah obaervsra conclude chut certain alkalia when present In the duat along with the free ailica would greatly lntenalfy Ita action. Theae obaervatlona were aade with respect to soap powder works. However, tneae latter findinga have not bt-cn aubatAntlated and are atiU open to queation. I encloae a couple of reprinta which you nay find of aoae lntoreat. I will be glad to heir fro* you further if I can he of any eervice. Sincerely youra. A* lanaa, M.D. V-' As aiatant Medical Director