The San Francisco call., 1898-07-10

N OCTOR ERNEST s. PILLS
 BURY, curator of bacteriology,
 of the College of Physicians and
 Surgeons, has been working for
 some weeks past on an exami- nation of the dust to be found in the air and on the streets of San Francisco. He has made microscope slides of dust found in all parts of the city from Pa cific Heights to the water front, and from North Beach to Butchertown. Of course a large variety of results was obtained, and the conclusions reached are most interesting and important. In a few instances some dangers are shown to be not so great as we have been in the habit of supposing. On the other hand a number of new dangers have presented themselves, and the air of San Francisco in the downtown dis tricts is shown to be about as foul as it can well be without starting a plague. Indeed by a comparison with the statistics of a similar work in other cities San Fr; ,ncisco Is shown to be in some respects the dirtiest in the world. While 1t lacks the soot and grime of Pittsburg it more thar makes up for 1t by a large number of dangerous mi crobes produced princi-ally from horse refuse.
 In making lis examination Dr. Pills bury made use of the most approved modern methods, and obtained positive results In each case. He used two modes of procedure. One was a direct examination Of the dust scraped be- tween the cobbles; the other an exami- nation of the organisms found floating about in the air too small to be seen by any but the most powerful micro scopes, and requiring the most careful handling to ,-Scertain their exact na- ture.
 The direct examination of the dust is a method very simple and easy to un- derStand. The examination of the aiI is very complicated, and requires the highest class of laboratory apparatus This is also somewhat long and easily interfered with.
 In the direct examination of the dust of the street very small quantity Is scraped up and put into an air tight bottle It is then taken U the labora- tory, and the finest of it sifted out A portion of this no larger than pin s head is spread over microscope glass slide, being held in place by thin, gummy Varnish. In this condition 1t is such small quantity it can scarcely De seen, and even the staining Tn strong aniline dye scarcely serves to make it more visible
 But when this plate is put under the objective of a ~owerful miscroscope 1t at once becomes a marvel.
 Dust and germs are taken from the air by means of what IS known as the Petri plate" This piece of apparatus really consists of fiat glass dish with a glass cover made to fit tight by be- Ing ground on the edges.
 In order to use this plate 1t is neces- sary 10 first prepare a culture medium oI gelatine and bouillon. This is done ny simply mixing the requisite quan- tlty or each and heating and stirring several minutes. While still hot this IS poured on the glass dish, which has Iirst been sterilized and cleaned and the cover placed on the top. It is then set aside to cool and after a few days shouid no poi of infection be visible on the gelatine which can be seen through the glass cover, it is ready for use. It is now known to be absolutely pure.
 The method of using these plates is to take them to the spot it is desired to test the air of and uncover them fo, . minute. The immediate effect ie not apparent. Sand, hair and other visihIa particles do not stick to ii and wha,, the plate is covered up 1t looks exactly as 1t did before 1t was opened.
 After exposure the plate is taken to