Diphtheria may occur at any time of the year, though it is more frequent during the cold months. The incubation, or the length of time between exposure to the disease and the development of the symptoms, is between two and five days. In its mild form the disease may be present without giving any constitutional symptoms. In its severe form, however, it is one of the most dangerous diseases of childhood. In large cities it is present all the year round with more or less frequent outbreaks in the form of local epidemics. In the country it is only seen in its epidemic form. It does not arise without a cause, that is, there is always a preceding case from which an epidemic springs, though it is not always easy to trace the connection. The child inhales the bacilli which cause the disease with the air it breathes. The bacilli may lodge on toys or other articles from which the child gets them. Direct infection is usually the mode of communication through which a child obtains the disease. The saliva and mucus from the nose contain the bacilli in large quantities and if a patient coughs or sneezes they are expelled in this way and infect others. Frequently a child suffering from a mild form of diphtheria may attend school and infect others without it being known that the child has the disease. Symptoms.--The symptoms vary with the severity of the attack. There are mild cases, as has been stated, that give no constitutional symptoms. There may be a small amount of local disturbance in the throat or nose and there may be some membrane present, but, for some reason, there does not seem to be any absorption of the poison into the system and the child escapes the systemic disturbance. Even as a local condition these cases vary. There is always a fever at the beginning, but the child never seems sick enough to go to bed. If the throat is examined it will be found to be red and slightly inflamed, there may be spots on the tonsils, or there may be a gray film over them. There is no discharge from the nose and the child does not complain of an excess of mucus from the throat. The spots may last for a week and then disappear. These cases are difficult to diagnose without making a culture, and if the physician insists upon keeping the child confined to bed while apparently well the family as a rule object, though it is absolutely necessary. These are the cases that do great harm in school, and no mother should object if the physician insists in taking preventative measures to stop an epidemic if the bacilli have been found in the child's throat. She should rather feel thankful that the child escaped so easily.