Fourthly, albuminuria, which is common in diphtheria, is said to be rare in membranous croup. But this is not altogether the fact. More over, albumen does not always appear in the urine at the beginning of an attack of diphtheria, but may be delayed for several days. Now the dura tion of fatal cases of croup is often terribly short ; so that the patient may die before the albuminuria has had time to occur.
Lastly, paralysis is a not uncommon sequel of diphtheria, while in croup it is very rare. But it must be remembered that true membranous croup is an excessively fatal disease and comparatively few cases recover. Even as a consequence of diphtheria the occurrence of par alysis is variable in different epidemics ; and taking the milder cases with the severer, the proportion has been estimated by Dr. Greenfield at no more than one in twelve. In convalescents from membranous croup the proportion who are likely to suffer from paralysis would, therefore, under any circumstances be very small.
From consideration of the above facts and arguments the only conclu sion to be drawn is that a large proportion of cases of membranous croup are cases of laryngeal diphtheria. It does not, however, follow that mem Iranous laryngitis is never due to any other cause than the diphtheritic poison. The child's larynx is especially prone to membranous inflammation ; -and if, as has been positively stated, a true false membrane may be set by burns, scalds, and other irritants to the air-passages, it is possible that the disease may occasionally occur independently of the diphtheritic virus.
Diphtheria is met with both as an epidemic and as an endemic disease, -and varies much in character and severity at different times and in differ ent localities. It may attack children who are apparently in robust health, may arise in cachectic subjects, or appear as a sequel of severe general dis ease. Like typhoid fever the disorder is apt to occur more than once in the same individual, for the protection it affords against a recurrence is by no means complete. Sometimes the second illness may be more severe than the first, for a child who has passed safely through one attack may succumb to a second.
Causation.—On account of the susceptibility to diphtheria in early life, childhood may be considered to be one of the predisposing causes of the malady. Infants under twelve mouths of age are not often attacked ; but after that age and up to the fifth or sixth year the disease is frequently met with. After the sixth year it again becomes less common, and is com
paratively rare in the adult. Besides this natural susceptibility, there is probably in many cases a special susceptibility inherent in the constitution of the patient. Sometimes whole families are cut off during an epidemic of the distemper. Sometimes successive children of the same parents fall victims to the disease at various times and in different places ; and in many cases this unfortunate predisposition appears to be a hereditary defect. Besides these general causes, special delicacy of the throat may render the child more sensitive to the diphtheritic poison, inclining him to take the disease where a stronger subject would escape altogether. Also the pres ence of a catarrhal condition of the faeces at the time of exposure to the unhealthy influence increases the likelihood of infection. The scrofulous . constitution has been said to induce a susceptibility to the diphtheritic virus ; and there is no doubt that the subjects of this diathesis are, as a rule, keenly sensitive to all forms of zymotic poison.
Cold and moisture appear to have some influence in quickening the ac tivity of the contagious principle, for the disease is common in country dis tricts, especially in damp places, and is more prevalent during the winter months than at any other period of the year.
With regard to the exciting causes : There can be no question as to the highly poisonous nature of the exudation from the affected surfaces, for the discharges have often communicated the disease by coming into contact with a healthy mucous membrane. The virus may, however, be also con veyed by more subtle emanations from the affected person ; and it is be lieved that the contagious principle may be carried to a distance in the clothes of the patient himself after convalescence, or in the dress of a nurse who has not herself suffered from the disorder. Indeed, all the sur roundings of the patient appear for some time to be capable of communi cating the disease. It is even stated that in certain cases a convalescent may be still the channel through which the diphtheritic virus is conveyed to exceptionally susceptible subjects, although a period of months has elapsed since recovery from the disorder ; but in such a case it would be difficult to exclude other and more recent sources of infection.