All observations made on an extensive scale show that the female sex is the more largely involved. From 1890 to 1901, 6666 girls as against 5127 boys were officially recorded in Vienna as having been affected with whooping-cough.
While in large cities pertussis never disappears entirely and the preponderating involvement of the first years of life in the morbidity of whooping-cough may be regarded as the expression of a general sus ceptibility of man, to which even the very youngest are subject, remote countries, cut off from the outside world (e.g. the Faroe Islands), arc apt to become rapidly infected from a single exposure and to suffer a general dissemination of the disease. The immunity acquired by a large percentage of persons who early in life have had an attack, as well as a certain reduction of their susceptibility. affords a protection to adults.
Attempts made in various quarters from observations extending over decades to determine a certain periodicity for the epidemics of whooping-cough have not led to any satisfactory conclusions. Neither season nor weather nor other conditions such as the increased contact of children at the beginning of school, appear to occasion an epidemic like expansion of the morbidity curves.
Figures arranged according to months showing the number of eases of whooping-cough officially recorded in Vienna during five years (1S98 to 1902) exhibit the highest number for March (1332) and April (1243), the lowest for October (555). Other observers, however, report differently.
It seems that the raw periods of the year more frequently cause an increase in the morbidity figures and a protracted duration of single epi demics, corresponding to the deleterious influence exercised by inclement weather in general on affections of the respiratory tract. The alterna tion of measles and whooping-cough epidemics, sometimes observed but often overestimated as to its frequency, may possibly be accounted for in a similar manner. In both infectious diseases a distinct involvement of the respiratory tract is a prominent feature; in both, the portal of entrance of the pathogenic factor is presumed to be in the mucous mem brane of the respiratory tract. Thus a catarrh accompanying one of
these diseases might easily facilitate an infection with the other.
Since the disease has been completely described symptomatically, attempts based on anatomical and clinical experience have been made to investigate the etiology and pathogenesis of whooping-cough. The favorable prognosis of uncomplicated cases prevents obtaining post mortem findings undoubtedly underlying the basal disease. After death, we find almost always lobular-pneumonia and tuberculous alterations of the lungs and lymph-nodes, together with evidences of pulmonary em physema, dilatation and hypertrophy of the heart, changes in the cen tral nervous system (see nervous complications) capillary haemorrhages, etc., according to the clinical complications. The ever-present catarrh of the respiratory mucous membrane and its localization as may be deter mined laryngoscopically during life should support the theory that whooping-cough is a specific catarrh causing because of its localization, a spasmodic cough. However, laryngoscopic findings, credited almost exclusively to older investigators, differ quite considerably, both with regard to the intensity and especially the localization of the alterations. But it seems that the rima glottidis posterior is the point of irritation at which the tenacious little lumps of sputum, rich in mucin, driven up from the deeper bronchial branches by the movements of ciliated epithelium, excite the paroxysm.
Against the conception of whooping-cough as a specific laryngo tracheitis, the following facts have been justly brought forward: the rhythmic process of each paroxysm and of the whole affection differing from such catarrhs, the influence exercised on the symptoms by the state of mind, the convulsion phenomena during and between the individual attacks, and finally the frequent inactivity of narcotics, especially in the catarrhal stage. These facts were more apt to cause whooping-cough to be numbered among the functional nervous diseases. But its acute onset and undoubted contagiousness as shown by every day observations make the inclusion of pertussis among the contagious infectious diseases the only justifiable one.