MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 823 



and streptococcus. There is evidence supporting the theory of a fil- 

 trable virus; a bacillus of the haemorrhagic septicaemia group has been 

 described as a probable cause; various cocci and a symbiotic combina- 

 tion of organisms have also been suggested. At the present writing 

 the specific infective agent must be regarded as unknown. 



Some question the identity of the recent influenza with the former 

 disease of the same name epidemic in 1889 to 1892, but the term has 

 been rather loosely used in the interval, and it seems probable that we 

 have had a recurrence of the original disease but in more virulent form. 



Spain is given by some as the place of origin of this last outbreak 

 (whence the term " Spanish Flu"), and, if true, it seems worthy of note 

 that, after a quiescence of twenty years, the epidemic revived in a neutral 

 country rather than in a war-swept country where some sections of the 

 population were living under abnormal conditions of nutrition and 

 sanitation. Once started, however, war conditions certainly hastened 

 its spread, testified by the explosiveness of some of the outbreaks in 

 the armies where the intimate contact of large groups of men was so 

 much greater than in civil life. The swift passage from person to 

 person thus afforded to the specific virus and its concomitant organisms 

 may to some extent explain the remarkable virulence finally attained. 



The natural disease probably occurs only in man. Reports of 

 epidemics among animals have not yet had scientific confirmation, and 

 the experimental disease in the monkey needs further study. 



The incubation period varies from about one to seven days. 



The milder type of influenza which occurred in the spring of 1918 

 both in Europe and America, seems more likely to have been the pure 

 infection than the more fatal kind appearing in the following autumn 

 and winter. The initial stages were practically the same in the two 

 types, but in the winter type signs of lung involvement developed with 

 greater or less rapidity. 



The onset is sudden, with headache, pains in the back and limbs, 

 chilliness, dry throat, suffusion of the face and conjunctivas, and occa- 

 sionally nose-bleed. The temperature will range from 100 to io4F. 

 within a few hours but the pulse remains relatively slow; in many 

 groups of cases the blood-pressure has been uniformly low. The 

 leucocyte count is below or at normal with a relative increase of lym- 

 phocytes. This may give place later to a total and neutrophilic in- 

 crease as pneumonia develops. Cough may be absent at onset but 



