outbreaks of respiratory catarrh more remote in time and about the distribution of which less is known. It is not applicable to the sporadic cases or even the localized epidemics of respiratory catarrh to which the name influenza has been so often applied, especially in the years following fairly closely upon pandemic outbursts. In the years 1908, 1909, and 1915, for instance, un- usually large numbers of deaths were returned in London under the heading of " influenza." For the average Londoner, however, there was no influenza in these years; but the average Londoner and, indeed, the average inhabitant of Europe, Asia, Africa, and America, is quite alive to the fact that influenza prevailed in 1918-9. Statistical records of influenza mortality are apt to be very misleading as medical men often apply this name to fatal respiratory diseases of indeterminate symptomatology. When the real influenza comes, the public is at once aware of the fact because nearly everyone either gets infected or sees friends or relations infected within a very short space of time.
The Influenza Pandemic of 1918-9. This pandemic swept over the world in three successive waves, the first appearing quite suddenly in May and June 1918, the second starting at the end of Sept. or early in Oct. and waning in Dec., and the third wave, less uniform in character, appeared early in March 1919.
First Wave. This outbreak, attributed by France to Spain, by Spain to France and by America to eastern Europe, seems to have appeared almost simultaneously amongst the nations of the " En- tente" arrayed against the enemy on the western front, and amongst all those communities in intimate touch with them. In the armies of the Entente in France, Belgium, and Italy; in the military camps in England and America; in the civilian populations of England, France. Italy, Spain, and Portugal; in transports at sea; in the closely linked theatres of war of Salonika and Egypt, and in Gib- raltar, Malta, and India itself, the outbreak of influenza showed the explosive character that is only possible for a highly invasive infec- tion assisted by conditions of swift inter-communication, such as obtain in modern war.
The invisible barriers of hostility or neutral exclusion seem to have imposed a slight check on its spread so that this first wave made its appearance a little later amongst the Central Powers and their neighbours. It was not until early in July that it attained its full proportions in Germany, Austria, Norway, Sweden and Den- mark, Holland and Switzerland. In several large areas of the world's surface, this first wave seems to have been absent or so slight as to have escaped record. In the South American republics, in Bermuda, the British West Indies, the Azores and in the islands on the Pacific, the summer of 1918 seems to have passed without an influenzal outbreak. The same appears to be true of Australia and New Zealand, though cases are said to have appeared in the latter in Aug., the harbingers, perhaps, of the autumn, rather than the first manifestations of the summer, wave.
This first wave passed rapidly, so that a "frequency curve" by weeks, in which the incidence in the worst week is taken as 100%, shows a steep ascent to a maximum, followed by an equally steep and almost symmetrical fall, the whole episode passing within about five or six weeks. So benign was the type that many cases among soldiers at the battle-front escaped record, as the men never " re- ported sick " but merely rested for a day or so in their units, and this was fortunate as the army hospitals were soon overcrowded. The death-rate was inconsiderable, but there was an ominous tendency to a higher mortality amongst the later cases, just before the wave came to an end, seeming to suggest an increase in virulence. The clinical picture cannot be better summed up than in the words of a consultant physician in France who, describing the first batch of cases, exclaimed " it is like a mild attack of measles without a rash." Respiratory catarrh, congested conjunctivae, headache, lassitude, pyrexia of short duration, a feeling of prostration with the return of temperature to normal, and then a rapid recovery, of health ; such was the course in the vast majority of the cases during the first wave. Complications were almost unknown during this outbreak; but a few cases developed broncho-pneumonia or haemorrhagic oedema of the lungs towards the end of the wave, and it was these cases that sent up the case-mortality. In all these characters, the first wave closely resembled the outbreak of 1890. In one re- spect it showed an interesting difference. Whereas in 1890 the death- rate was greatest amongst the middle-aged and elderly, in 1918 the chief sufferers were amongst the " young adult " groups.
Second Wave. Towards the end of Sept., or early in Oct., the second wave suddenly gathered force and swept over the world; the crowning tragedy of so many tragic years. Soldiers, miracu- lously spared in battle and for whom hope was now dawning with the promise of victory; youths at school or college, to whom the future might look to fill the gaps of war in years of peace : these were the harvest chosen for the scythe of the Angel of Death. For the character of the pandemic had changed and the benign attacks of the summer now gave place to the terrible scourge of the autumn
outbreak. Geographically, this wave was almost universally felt, and it seemed to mount up simultaneously throughout the world. St. Helena is said to have escaped. Mauritius, too, had a reprieve ; and it appears to be true that the quarantine measures applied by Australia were successful for the moment, but throughout Europe, America, Asia and Africa, this fatal pandemic held undisputed sway. The upward curve of morbidity was almost precisely similar to that of the summer and the maximum was reached as quickly as in the previous wave, but the fall was much slower and less regular. The outstanding difference between the two waves was the marked tendency to pulmonary complications and the high death-rate of the second. The singularly uniform syndrome of the summer epidemic gave place, in the autumn, to several varieties of clinical picture de- pending on varying combinations of several factors, amongst which might be reckoned the virulence of the microbic invader, the resis- tance of the patient, the nature of the bacterial flora of his respira- tory tract, and environmental conditions such as occupation, wages and housing. As a rule, the attack was ushered in by the catarrhal and pyrexial symptoms noted in May and June. In many cases, especially where circumstances permitted of immediate rest and treatment, the disease took a favourable course towards recovery, although prostration was nearly always a more marked feature than in the summer. In others, the story was different. The early pyrexial catarrh was sometimes followed by intense toxaemia leading so rapidly to a fatal issue that there was no time for pulmonary complications to develop. But in a very large number of cases the lungs became severely affected and the patient passed into a state of anoxaemia recalling that produced by exposure to the " pulmonary irritants" of gas warfare. But there was a formidable difference between the two conditions. While the " phosgene " patient had to deal with a sterile exudate, evoked by a chemical irritant and ca- pable of rapid absorption if vitality was maintained, the lungs of the influenza patient were charged with an exudate evoked by a living virus which had already overcome tissue resistance and could offer to " secondary invaders " conditions of symbiosis favourable to their growth. Here lay the danger. The virus of influenza could open, as it were, the door to the streptococci, pneumococci, staphylococci and other organisms normally held within safe numerical limits upon the respiratory mucous membranes.
Those who wish to be fully informed of the clinical features of this phase of the disease cannot do better than turn to the admirable account of it given by Dr. Herbert French in the " Report on the Pandemic of Influenza, 1918-9," published by the British Ministry of Health in 1920. The appearance of the patient was often very characteristic. Lying quietly in bed without any of the agonized and restless dyspnoea of the "chlorine-gassed" case, he might seem to the superficial observer to be not very ill. But a closer examination would note the dull cyanosis of the lips and ears, the livid pallor of the face, the rapid shallow respiration ; while the pulse, though some- times good, was often " running " and feeble, indicative of toxic action on the heart muscle. In such a case wisdom lay in sparing the patient the fatigue of a comprehensive examination of the chest. The mere effort of sitting forward or turning over, to allow of stetho- scopic investigation of the bases of the lungs, was sometimes enough to turn the scale against the sufferer. Where, however, an examina- tion was carried out, it frequently afforded but little information beyond the fact that there was a marked diminution of the breath sounds and a loss of the vesicular quality of respiration. The post- mortem appearances, while tending to have certain basal characters in common, varied considerably with the nature of the " secondary invaders " and other factors. In nearly all cases, there was a hsemor- rhagic tendency not often seen in other acute lung affections; and this sometimes amounted to a haemorrhagic oedema involving the greater part of both lungs. " Wet lungs," " dripping lungs," were expressions frequently heard in the post-mortem room. Areas suggesting haemorrhagic infarcts with their bases extending under the pleura were often noticed. The cut surface of the lungs showed, as a rule, peri-bronchiolitis and patches of broncho-pneumonia with a general state of oedema throughout the parenchyma of the lung; or a whole lobe might give the appearances of red or, in older cases, grey hepatization. (For a detailed account of these appearances, together with their morbid histology, see the article by Maj. Tytler, C.A.M.C., in " Special Report Series No. 36 " of the Medical Research Council, 1919.)
Third Wane. The third wave had no distinctive characters. It tended to resemble the first wave rather than the second, though pulmonary complications and fatal cases were fairly numerous.
Etiology. As to the causative organism of influenza we remain, after the greatest pandemic in history, still in doubt. This is no reproach to the science of bacteriology. A moment's reflection will show that research, to give conclusive results, must be carried out during the outbreak at a moment when the " pan- demic" character gives the stamp of certainty to the diagnosis and the infectivity of the cases is at its height. But so swift is the passage of the wave that it is over by the time that the necessary workers, equipment and accommodation for investigation have been provided. Before 1918 few doubted that the Bacillus
