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The diphtheria antitoxin which is now extensively and successfully used in the specific treatment of the disease may also be used to prevent its development in persons exposed to infection. From five to ten cubic centimetres of a reliable antitoxin is used for this purpose. This is injected subcutaneously and is a harmless procedure which has been proved to be efficacious in most cases, or at least to greatly modify the severity if an attack occurs. Where children have been exposed to infection, or under circumstances which prevent the proper isolation of a diphtheria patient, it is prudent to resort to such preventive inoculations. As is generally known, the antitoxin is usually obtained for practical purposes from horses which have been rendered immune by repeated and gradually increasing doses of diphtheria toxin—that is, the poisonous substance developed by the diphtheria bacillus during its growth in suitable culture media. The antitoxin is contained in the blood of the immune animal, and the clear blood serum which separates on standing, from the “clot," which contains the red and white blood corpuscles, is spoken of as “antitoxin” and is used in the treatment and prevention of the disease. From this blood serum a more concentrated antitoxin may be obtained by chemical methods, but this has not come into practical use.
EPIDEMIC influenza (“la grippe ") is an infec
tious disease due to a minute bacillus discovered by the German bacteriologist Pfeiffer in 1892. This bacillus is found in great numbers in the purulent bronchial secretion coughed up by persons suffering from influenza and the disease is propagated by contact with the sick and with articles infected by them, just as is the case in diphtheria, or whooping-cough. The rapid extension and wide prevalence of the disease is due to the facts that persons of all ages are susceptible, and that isolation of the sick and disinfection of sputa are rarely practised, on account of its comparatively mild character. Nevertheless, the disease is attended with considerable danger, especially for old persons or those in feeble health; and it is the direct or remote cause of many deaths. The official records of Prussia for 1892 show a mortality from this disease of 15,911, of whom over half were more than sixty years of age. The total number of deaths in the United States during the census year 1900 was 16,645. As in Germany and elsewhere a large proportion of the deaths occurred in persons over sixty years of age or among young children, under five. But these figures by no means represent the total mortality from the disease. Many deaths re
Fig. 8. Bacillus of influenza ; magnified 1000 diameters.
corded as due to pneumonia are the result of a preceding attack of influenza. Other complications or results of the disease which may have a fatal termination are connected with the brain and spinal cord, the heart or the kidneys. Serious eye and ear troubles, also, not infrequently follow an attack of influenza.
Wide-spread epidemics of influenza have prevailed in Europe from an early period. It prevailed in Italy,
Germany, and England as long ago as 1173, and since that time there have been repeated epidemics. The epidemic which started in first one occurring in the British Islands of which we have authentic and accurate accounts. This epidemic had such a wide distribution that it is said to have “raged all over Europe, not missing a family and scarce a person ” (Thomas Short).
Another still greater epidemic, or “pandemic,” dates from the year 1580. We cannot spare the space for an historical account of the numerous epidemics which occurred during the seventeenth and eighteenth centuries, but will pass on to the nineteenth.
In 1802 the disease inade its appearance in France and during the following year obtained wide extension in European countries. In 1807 it was generally disseminated in North America. It again prevailed both in North and South America in 1815 and 1816; the next epidemic in the United States was inaugurated in 1824 and lasted for several years. The epidemic of 1833 was apparently confined to the Eastern Hemisphere, where the countries of Europe, Asia, and Northern Africa were invaded. It is said that in St. Petersburg “not one person escaped the influenza” during this epidemic. The next extensive epidemic in Europe was during the years 1836–37 ;
and again the Eastern Hemisphere was visited in 1847–48. In the winter of 1851 the disease obtained wide prevalence both in North and South America. In 1857–58 it again prevailed extensively in both hemispheres and in some localities (Rome and Naples) was attended with a high rate of mortality. During the winter of 1874-75 it again prevailed extensively in Europe and America. During the epidemic of 1889-90 the disease obtained, within a brief period, a wider extension in all parts of the world than in any previous epidemic. This pandemic apparently had its origin in Central Asia. The United States has not been free from the disease since the date last mentioned, and some very susceptible individuals, especially in cities, suffer an attack almost annually.
The incubation period is comparatively brief, being from two to six days. Those whose occupation keeps them out-of-doors during the daytime are less subject to attack than factory hands or others, who are more exposed to contagion by reason of their living in closed rooms containing numerous occupants. The disease prevails to some extent throughout the year but the largest number of cases occur during the winter and spring months. Catarrhal conditions of the bronchial and nasal mucous membranes, and the meteorological conditions which are favourable to “catching cold” constitute predisposing causes. Per