{260} A number of flies may deposit their ova in wounds or in such of the body cavities as they can reach, and the resulting maggots may cause intense irritation. Ova may be swallowed with the food and the maggots appear in the feces. Probably most important is the "screw worm," the larva of _Compsomyia macellaria_, infection with which is not rare in some parts of the United States. The ova are most commonly deposited in the nasal passages, and the larvæ, which may be present in great numbers, burrow through the soft parts, cartilage, and even bone, always with serious and often with fatal results. {261} CHAPTER VII MISCELLANEOUS EXAMINATIONS PUS Pus contains much granular débris and numerous more or less degenerated cells, the great majority being polymorphonuclear leukocytes--so-called "pus-corpuscles." Eosinophilic leukocytes are common in gonorrheal pus and in asthmatic sputum. Examination of pus is directed chiefly to detection of bacteria. When very few bacteria are present, culture methods must be resorted to, but such methods do not come within the scope of this work. When considerable numbers are present, they can be detected and often identified in cover-glass smears. Several smears should be made, dried, and fixed as described under Sputum (p. 32). One of these should be stained one-fourth to one-half minute with Löffler's methylene-blue, rinsed well with water, dried, mounted, and examined with an oil-immersion lens. This will show all bacteria except the tubercle bacillus, and often no other stain is necessary for their identification. In many cases special stains must be applied. _Gram's method_ (p. 40) is a very useful aid in distinguishing certain bacteria. The more important organisms react to this staining method as follows: {262} GRAM STAINING GRAM DECOLORIZING (Deep purple). (Colorless, unless a counterstain is used). Staphylococcus. Gonococcus. Streptococcus. Meningococcus. Pneumococcus. Bacillus of influenza. Bacillus diphtheriæ. Typhoid bacillus. Bacillus tuberculosis. Bacillus coli communis. Bacillus of anthrax. Spirillum of Asiatic cholera. Bacillus of tetanus. Bacillus pyocyaneus. Bacillus aërogenes capsulatus. Bacillus of Friedländer. Koch-Weeks bacillus. Bacillus of Morax-Axenfeld. [Illustration: FIG. 113.--Staphylococcus pyogenes albus from an abscess of the parotid gland (Jakob).]