Anything which impairs the vital functions will predispose to an attack of any febrile or other disease. We do not purpose to mention here all the numerous causes of impaired vitality, but only some of those especially active in rendering the system liable to the disease under consideration.

"Taking cold" is a process very difficult to describe exactly, but is so common an occurrence that the phrase is significant to every one. In general, when a person has taken a cold there is more or less congestion and irritation, if not actual inflammation, of the mucous membrane of the pharynx, and often of the nasal cavity also. There is also usually present an increased secretion of these parts, and a tumid condition of the mucous membrane. This condition is particularly favorable, not only to the lodgment and development of the diphtheria germs, but to the development of the accompanying inflammation.

Chronic inflammation, or catarrh of the pharynx, as well as nasal catarrh, is also a powerfully predisposing cause of diphtheritic inflammation of those parts. When the mucous membrane is already affected by an inflammatory process, the presence of the diphtheria organisms is all that is required to convert the morbid process into a diphtheritic inflammation. Consequently, those who are thus suffering should be exceedingly careful to avoid any sort of exposure to infection from the disease. Persons who have been subject to pharyngeal catarrh find the difficulty increased after an attack of diphtheria

Insanitary conditions, by impairing the vital forces, and thus diminishing the vital resistance of the tissues, will produce a strong predisposition to diphtheria. As already shown, all sources of decay may be sources of diphtheria poisoning, so that insanitary conditions are both directly and indirectly productive of this dangerous malady. This fact is well worthy of repeated emphasis when the larynx becomes affected, while adults may suffer the same amount of infection and invasion of the throat and larynx without any serious interruption of respiration. This is one cause for the greater fatality of the disease in children.

The disease is often more prevalent in the cooler seasons of the year than in the summer, but probably this fact is wholly due to the increase of predisposing influences of other sorts at those times, as increased frequency of colds and nasal and pharyngeal catarrhs; less free circulation of air in dwelling-houses greatly increasing the virulence of the poison wherever it may chance to be at work, and similar incidental causes. The disease has been known, in many instances, to extend its ravages in certain localities as widely and as fatally during the heat of summer as at any other season of the year.

The observations compiled by Dr. H. B. Baker, Secretary of the State Board of Health of Michigan, show an increase in the frequency of the disease during July and August. This may be due to the fact that the great heat of those months encourages decomposition and the generation of germs in unusual abundance.

Certain diseases, as whooping-cough, typhoid fever, and scarlatina, are liable to be followed by diphtheria, which is then known as secondary diphtheria. Children under ten years of age show a marked susceptibility to this disease. Between the ages of two and four years the susceptibility is greatest. Children under one year of age are not likely to have the disease. Very young children seem to be almost wholly protected against it by their infancy. Children are not only the most liable to take the disease, but they are likely to suffer the most severely. Adults, except in cases of extreme old age, suffer much less from the most serious results of the disease on account of greater size of the laxynx. In children the larynx is so small that suffocation is imminent.

A mild or catarrhal form of the disease is very likely to be overlooked, or regarded as only an ordinary sore throat, even by physicians. Some physicians contend that the catarrhal form of diphtheria does not exist. We would call especial attention to the fact that epidemics of diphtheria are always accompanied and followed by numerous cases of sore throat, tonsilitis, etc. Dr. Arthur Downs, in an able article in the American Medical Bi-Weekly, takes the position that these affections at such times are " essentially identical with undoubted diphtheria" The reasons he gives for thus thinking are as follows:"1. These sore throats prevail correlatively with the unquestioned cases of diphtheria 2. Under favorable conditions they may communicate the typical form of the disease. 3. The latter, also, in its turn, gives rise to these apparently trivial sore throats." Dr. Downs adds "I can only repeat my conviction that, if the public generally, and medical men in particular, dropping the misleading name derived from a variable pathological appearance, would regard these concomitant 'sore throats' as essentially 'diphtheritic,' a great point would he gained toward the isolation so necessary, but at present so difficult to obtain. It is to this end that Dr. Thursfield, whose experience is second to none, strenuously urges the disuse of the modem term 'diphtheria,' and the resumption of the old name 'contagious cynanche.' "