THE MICROSCOPE IN MEDICINE AND SANITATION. 121 
in a frame and provided with screws, by which they can 
be pressed together, thus reducing the meat to a thin 
transparent layer. The frame bears on its under side 
two ridges which fit into grooves in a special corrugated 
stage of large size on the microscopes designed for this 
purpose. Under a very low objective, of 1}-inch equiva- 
lent focus, the compressed frame is then examined, being 
slid along until its whole width has been covered, and then 
shifted to the next groove, so that a new field may be 
examined. In this way the whole sample may be viewed 
in five minutes by a trained observer. 
Under the microscope the pork is seen to be made up 
of the long cylindrical cross-striated fibres of voluntary 
muscle, and if Trichina be present the cysts will be seen 
here and there as spindle-shaped, whitish bodies. In 
sections of trichinous pork prepared after paraffin im- 
bedding with the microtome, the worms may be seen 
coiled up inside the cysts, as shown in Fig. 47. 
9. The Microscopy of Drinking Water.—The sanitary 
quality of water depends primarily upon the presence 
or absence of disease germs, generally introduced in 
sewage. The most important evidence as to its character 
is therefore obtained by the bacteriological and chemical 
analyses, which indicate with great delicacy the presence 
of minute traces of sewage pollution. A microscopical 
examination may, however, often add information of 
value by showing the presence of starch-grains, yeast- 
cells, fragments of vegetable tissue, and certain Infusoria 
characteristic of decomposing material; organisms pecul- 
jar to a particular pond or stream have sometimes proved 
