. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . FiG. 23.—The Winchester quart bottle with label affixed. exposed to light until the analysis is commenced, andunder no circumstances should the major part of theanalysis be delayed more than 48 hours, or importantchemical changes may transpire. Although information is often furnished, and gene-rally demanded, on all the points bearing upon thepossibilities of pollution which the water has incurred,it is often best not to avail o
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . FiG. 23.—The Winchester quart bottle with label affixed. exposed to light until the analysis is commenced, andunder no circumstances should the major part of theanalysis be delayed more than 48 hours, or importantchemical changes may transpire. Although information is often furnished, and gene-rally demanded, on all the points bearing upon thepossibilities of pollution which the water has incurred,it is often best not to avail oneself of the information COLLECTION OF SAMPLES. 25 until the analysis is completed, otherwise there is a strongincentive to treat cursorily some part of the analysis,on the supposition that it is unnecessary, which withdue care, might have disclosed an undreamt of sourceof pollution. Regarding such information, the mostimportant to the analyst would be that bearing uponthe constitution of the strata through or over which. Fig. 24.—Wicker case for the Winchester quart bottle. the water has passed, since certain ingredients (in de-fault of such a source) are indicative of organic pollu-tion ; unfortunately this is by far the most difficult in-formation to obtain in a reliable form. Comparatively,all other information is of little worth to the analysisitself, since contamination, past or present, will readily 26 LABORATORY WORK. be detected. It is important, however, to keep in viewthe fact that our work resides essentially in the causeof disease prevention, and that our duties and responsi-bilities do not end in returning an analytical report ;and that, as sanitarians, all information as regards therisks of pollution are of great value as indicating possi-bilities of danger, when such dangers may not be mademanifest at the time in an analysis; it is also of greatimportance to know, in every instance, the motive forrequiring an analysis, as one may often thus learn thepresenc
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