67 
gree by the passing traffic, fifty-three carriages, two bicycles and one 
horseback going by during the ten minutes’ exposure. The wind was 
very light. 
Another exposure was made when everything was dry, and after the 
wind had been strong and gusty for some hours, with the following results: 
MUCH UUM ee tetrateca lene cretals = starmta hearse ees eG SS we eee eee ee OOO 
Heel Clonee Srepe ne rah cheer cece ciciitoeeaeie eRccst tie eeere Ie eas Obie eS iaor cia) Reyer ee Olan ate 463 
WVOCGs blokes (UMERCOSOLCH)E a2 see cc cis c.c sos es ace ce snes 304 
SINGS ST Mal tea erereters ieee atone eraraperslea che oeaversisatsne ahold sus, cite erates levats 180 
Here the sheet asphalt had apparently been wind-swept, and was clean 
and dry. 
The averages of all exposures, excluding the midnight one, were as 
follows: 
WIR GRIST SS casdtoe oboe > SC PIANO Dots Le AOS enn nate mere tty: 
ECOL rsp levers tsetse Uns eueneialae veto te al siecle slniSYF st 2 2 nape acre 1084 
JST G SS 2 A tah Satie BR PeR Ie OILS CACCRD OR ROR DIR AR SORE Hn PRA ERE 960 
AVOCA MUM CreOS OLE) rs eewsievcisth ance velo sign. atere-< otaier Couele) © Gravee ane 561 
Therefore, if the amount of dust floating over any given pavement is 
a measure of the sanitary value, these pavements in question will take 
the following rank: wood, brick, sheet asphalt and macadam. The above 
averages include exposures under all kinds of varying conditions. 
While we do not feel that we can conclude anything very definite from 
these experiments, they seem to point to possible conclusions of value if 
pursued to the proper extent. Previous opinions commending or ¢con- 
demning any pavement from the sanitary standpoint lack scientific found- 
ation, and therefore are not to be seriously considered. In the experi- 
ments herein reported there are a number of factors that need to be more 
earefully determined, such as, that the bacteria that are caught on the 
agar plates actually come from the pavement ana not from the surround- 
ing lots and buildings; and furthermore, that these bacteria are of a patho- 
genic nature or not. These uncertain features are receiving careful atten- 
tion in our future experiments, and it is hoped that in their study will be 
found the key to the solution of these pavement problems. 
