Pseudomembranous conjunctivitis generally shows either _streptococci_ or _diphtheria bacilli_. In diagnosing diphtheric conjunctivitis, one must be on his guard against the {276} _xerosis bacillus_, which is a frequent inhabitant of the conjunctival sac in healthy persons, and which is identical morphologically with the diphtheria bacillus. The clinical picture is hence more significant than the microscopic findings. Various micro-organisms--bacteria, molds, protozoa--have been described in connection with trachoma, but the specific organism of the disease is not definitely known. THE EAR By far the most frequent exciting causes of acute otitis media are the pneumococcus and the streptococcus. The finding of other bacteria in the discharge generally indicates a secondary infection, except in cases complicating infectious diseases, such as typhoid fever, diphtheria, and influenza. Discharges which have continued for some time are practically always contaminated with the staphylococcus. The presence of the streptococcus should be a cause of uneasiness, since it much more frequently leads to mastoid disease and meningitis than does the pneumococcus. The staphylococcus, bacillus of Friedländer, colon bacillus, and Bacillus pyocyaneus may be met in chronic middle-ear disease. In tuberculous disease the tubercle bacillus is present in the discharge, but its detection offers some difficulties. It is rarely easy to find, and precautions must always be taken to exclude the smegma and other acid-fast bacilli (p. 35), which are especially liable to be present in the ear. Rather striking is the tendency of old squamous cells to retain the red stain, and fragments of such cells may mislead the unwary. {277} PARASITIC DISEASES OF THE SKIN Favus, tinea versicolor, and the various forms of ring-worm are caused by members of the fungus group. To demonstrate them, a crust or a hair from the affected area is softened with a few drops of 20 per cent. caustic soda solution, pressed out between a slide and cover, and examined with a one-sixth objective. They consist of a more or less dense network of hyphæ and numerous round or oval refractive spores. The cuts in standard works upon diseases of the skin will aid in differentiating the members of the group. MILK A large number of analyses of human and cow's milk are averaged by Holt as follows, Jersey milk being excluded because of its excessive fat: HUMAN MILK. COW'S MILK. Normal variations, Average, Average, per cent. per cent. per cent. Fat 3.00 to 5.00 4.00 3.50 Sugar 6.00 to 7.00 7.00 4.30 Proteids 1.00 to 2.25 1.50 4.00 Salts 0.18 to 0.25 0.20 0.70 Water 89.82 to 85.50 87.30 87.00 ------ ------ ------ ------ 100.00 100.00 100.00 100.00