By this term is especially meant exposure to sudden temperature changes. The body may sustain a very high or a very low outside temperature providing the change is gradual enough so that the heat-regulating mechanism may adapt itself properly to protect the body and maintain an even temperature within. A sudden change from a very warm room to a very cold atmosphere; a quick transportation from cold air to a superheated apartment; or a sudden draft of air whose temperature is sharply at variance with surrounding air and therefore with the condition of the body surface may have a very bad effect. The skin and mucous membranes of the body have become accustomed to a certain temperature; the change irritates them. And the immediate result is a motor reaction increasing subluxation in the same body segment in which the irritation is greatest and probably producing first an irritation of the nerves at the spine and then an inflammation of the exposed surface. Thus a “cold” is produced. One who has no subluxation affecting the respiratory tract--a rare degree of normality--may escape coryza, bronchitis, or pneumonia, the most common effects, but may suffer a congestion of the stomach walls or of other parts of the body. It is said that the cold “settled on the stomach.” The fact is that the motor reaction takes advantage of the weak parts of the spine and affects them most, like the pernicious habit of spine-stretching which used to prevail among Chiropractors. This explains why “cold in the head” is so very frequent. The fourth Cervical vertebra is situated at the middle point of the neck and is very freely movable and easily subluxated and, in fact, more often displaced than other Cervicals. Noxious or poisonous vapors may have an effect identical with that of sudden temperature change. Sleeping in an improperly ventilated room often appears to cause “cold.” Careful study of the part of the body exposed to draft, and of spino-organic connection, will show that in most instances the effect of such exposure is first felt in the same body segment. It is a well-known fact that not all people are “subject to colds.” One may be “subject to lung colds,” another to “cold in the head.” The susceptibility is entirely governed by the condition of the spine, the person having no middle Cervical subluxation being immune from coryza even though subjected to the same exposure which will produce it in others. The pollen of plants produces hay fever in the susceptible in much the same manner that draft produces coryza, both acting as secondary causes. BODILY EXCESSES In this division of secondary causes may be mentioned overwork, continuous loss of sleep, overeating, venereal excesses, etc.