The complications are usually dependent upon outside causes, and have nothing to do with the poison proper of whooping cough, as far as we can tell. There are some which depend on an inflammation of the mucous membrane, which may be limited to any portion of the respiratory tract or may extend throughout it. Complications may arise from mechanical obstruction to inspiration by the swollen mucous membrane or from plugs of tenacious mucus, which may cause pulmonary collapse and favor the development of catarrhal pneumonia, and later even of phthisis; or from impediments to free and easy expiration, whether from spasm of the bronchioles, from forcible compression of the thorax through reflex nervous irritation, or from other obstructions, all of which tend to produce emphysema. Disturbances of the circulation, in the brain or elsewhere, may proceed from thrombi or emboli and give rise to complications which will render fatal an otherwise mild form of the disease. The invariable disturbance of nutrition which accompanies every disease affecting the nervous system is apt to show itself in the breaking down of products which are simply inflammatory. Vomiting may be a most serious complication, both from its immediate and remote effects. It may be due to gastric catarrh, or more frequently to irritation of the pneumogastric nerve.
ETIOLOGY.—Very numerous theories have been advanced as to the nature of this interesting disease. Hufeland, Lebenstein, Pinel, Jahn, Todd, Cullen and a host of others have regarded it as essentially a neurosis. By many others it has been supposed to be due to a lesion of the brain or of its membranes, but careful investigation has established the fact that there is no lesion in whooping cough at all constant or characteristic. By still others, and especially by Gueneau de Mussy, it has been regarded as essentially an affection of the tracheo-bronchial glands, a bronchial adenopathy, causing irritation of the pneumogastrics and of their bronchial branches by pressure of the enlarged glands. We have, however, seen many post-mortem examinations of the bodies of children who have died of measles, where marked enlargement of these glands was constantly found, but where no symptoms of whooping cough had been present. There are indeed many features of the disease which seem inexplicable on any other theory than that the essential cause of whooping cough is a specific poison, and such is the view now generally adopted. This poison is capable of being carried by fomites, though as it is highly infectious it is often communicated through the atmosphere, and is most frequently conveyed from individual to individual. Dolan,1 who has recently published a very interesting and valuable monograph on this affection, quotes Linnæus, who ascribed it to the irritation of insects, as the author of the modern view that whooping cough is due to the presence of a peculiar microbe, though it must be conceded that as yet it has not been discovered. Most observers hold that the contagium is not in the blood, but that it resides in the secretions of the respiratory passages, and is most virulent during that stage of the disease when the secretion is abundant. Letzerich states that he has succeeded in producing whooping cough in rabbits by inoculating the trachea with the sputa of the human subject. Dolan obtained similar results by injecting the nasal secretions, and also by compelling rabbits to inhale air impregnated with decomposing sputa and vomit of patients suffering with the disease.
1 Dolan, Thos. M., Whooping Cough, London, 1882.
The following brief statement of his conclusions may be quoted as presenting the most important facts concerning the pathology of the disease:
1st. Pertussis depends on a specific poison or contagion; this is universally admitted.
2d. This contagion is active and highly infectious; this is also granted.
3d. The contagion is analogous to the contagia which produce splenic fever, measles, scarlatina, variola, etc.
4th. It has a peculiar determination to the lungs.
5th. Like all other contagia, it has its period of activity and decline.
6th. The period of greatest activity is in the first and second stages.