An influenza pneumonia may show the general prostration and cardiac weakness of plague. In influenza pneumonia we have an onset with the features of ordinary influenza, which, however, in the influenza epidemic in 1918 was often short. In plague pneumonia we have pneumonia from the start. The pulse in plague is early weak and rapid and the tendency to a stuporous state more marked. The early appearance of thin watery sputum, which quickly becomes blood-tinged and always contains plague bacilli is noted in plague pneumonia. Only a few hours elapse before we have bloody sputum which in influenza is a later and not constant sign. The dyspnoea is earlier and much more pronounced in the pneumonic plague. At autopsy Crowell notes the almost invariable presence of pleural exudates in plague while an acute vesicular emphysema is a feature of influenza pneumonia. Malaria and septicaemic conditions may be confused with septicaemic plague. The sudden onset and prostration of relapsing fever may make one think of plague. Many have thought climatic bubo a form of ambulant plague but the gradual onset, only slight tenderness of the swollen glands and slight prostration should differentiate. Venereal bubo cases are apt to be regarded with suspicion during epidemics. Markedly toxic cases of typhoid fever with an exceptionally rapid onset may give rise to confusion. =Laboratory Diagnosis.=—If the patient has a bubo we should introduce a hypodermic syringe needle into the swollen, oedematous glandular mass in order to obtain some of the gland juice. Smear a drop of this on a slide, stain with Loeffler’s blue or dilute carbol fuchsin and examine for bipolarly stained oval bacilli. When the bubo begins to soften we may not obtain plague bacilli. Probably the best stain for plague bacilli is that recommended by Archibald. There are two solutions, one made by dissolving 0.5 gram of thionin and 2.5 grams phenol crystals in a 1% aqueous solution of formalin; the other solution is made by dissolving 0.5 gram methylene blue and 2.5 grams phenol crystals in a 1% formalin solution. Let these stock solutions stand 24 hours before using and then mix equal parts of each solution; filter, and stain smear for 10 seconds. Wash and dry. In a case of suspected pneumonic plague we stain the smear of watery or thin blood-tinged sputum as above. The same procedure may be followed with a rather heavy blood smear of a drop of the 5 or 10 cc. taken from a vein for culturing in a case suspected of septicaemic plague.