Larrabee, R. C.: _Tobacco and the Heart_, Abstr. Jour. A. M. A., 1903, XLI, p. 50. Read before the Massachusetts Medical Society, June, 1903. Pel: _Un cas de psychose tabagique_, Ann. med. Chir., 1911, XIX, p. 171. SECTION VI AVOIDING COLDS [Sidenote: Infection] Bacteria play a part in most colds. In some cases there is a general infection, with local symptoms, as in grippe; in others there is a local infection, with mixed classes of bacteria. It is probable that these various forms of bacteria are constantly present in the nasal secretions, but do not cause trouble until the local resistance or the general resistance is in some way lowered. [Sidenote: Nasal Obstruction] In many, the susceptibility to colds is due to abnormalities in the nose or throat. Nasal obstruction is a very common condition. The nose, like the eye, is usually an imperfect organ. These obstructions are often the result of adenoids in childhood, which interfere with the proper development of the internal nasal structures. Malformation of the teeth and dental arches in childhood are frequent and often neglected causes of nasal obstruction. Such malformations are caused by the arresting of the growth of the upper jaw and nasal structures. Correction of the deformity of the arches often renders nasal surgery unnecessary. Such conditions not only predispose to colds, but increase their severity and the danger of complicating infection of the bony cavities in the skull that communicate with the nose. They also increase the liability to involvement of the middle ear and of the mastoid cells which are located in the skull just behind the ear. The importance, therefore, of having the nose and throat carefully examined, and of having any diseased condition of the mucous membrane or any obstruction corrected must be apparent. All who suffer from recurrent colds should take this precaution before winter sets in. [Sidenote: General Resistance] If the nasal passages are put in a healthy condition, strict obedience to the rules of individual hygiene will almost wholly prevent colds. In fact, except where actual nasal defects exist, the frequency of colds is usually a fair indication of how hygienically a person is living. The following points need especial emphasis, though they repeat in some cases what has already been said in the text. [Sidenote: Skin Training] It is a familiar fact that exposure and chilling will often produce a cold. This is usually due to the fact that the nerve centers controlling the circulation of the skin are over-sensitive, and exhibit a sort of hair-trigger reaction to exposure, causing a disturbance of the circulation, and of the heat-regulating machinery of the body of which the spongy shelf-like turbinated bones in the nose are an important part. Skin training, then, appears to be the first hygienic steps toward establishing a resistance to colds.