. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . by making these replace theabstracted fat (cream) of skimmed milk, this latter maybe turned to account. * Different samples of each of these cheeses vary considerably inthe percentage amounts of their constituents. f Very poor because made from milk which has been partiallyskimmed. 302 LABORATORY WORK. In this country, at the present day, it may be saidthat with the exception of colouring matter—which isgenerally annatto and har
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . by making these replace theabstracted fat (cream) of skimmed milk, this latter maybe turned to account. * Different samples of each of these cheeses vary considerably inthe percentage amounts of their constituents. f Very poor because made from milk which has been partiallyskimmed. 302 LABORATORY WORK. In this country, at the present day, it may be saidthat with the exception of colouring matter—which isgenerally annatto and harmless—the cheeses producedare pure. It has been shown, however, that in somecases (especially foreign cheeses) their surfaces have beenbrushed over with highly poisonous antiseptic solutions,such as arsenious acid and sulphate of copper—in orderto preserve them from attack by parasites and fromdecay; that colouring matters have also been used totint the rind ; and that those small and delicate cheeseswhich are wrapped in thin lead papers may take upthe metal. A careful examination, therefore, of therind for metallic poisons may be occasionally Fig. 51.—Aspergillus glaucus. Any starch employed—as it rarely is—as an adul-terant, can be detected by the iodine reaction and themicroscope. Cheese is peculiarly liable—and especially the moisterkinds—to parasitic growths, which are considered bymany to add materially to the flavour of the are probably harmless when ingested with thecheese; but a knowledge of the commoner forms ofgrowth is desirable : — Aspergilhis glaums is a form of vegetable fungus, andgives rise to the appearance popularly known as blue BUTTER CHEESE—TYROTOXICON. 505 mould —and sometimes also of green mould; underthe microscope its appearance is that denoted in fig. 51.
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