In the year 1908, Doerr^ announced the results of his experiments on the infectivity of the blood of the Dalmatian summer fever, and on the mode of the transmission of the virus by the phlebotomus. Since then the closely related ailments in Malta have been investigated in a similar manner. Tedeschi and Napolitant have made a similar enquiry into the nature of the Italian " summer influenza." Kilrov* has put to the test of experiment the causation of the fever as it occurs in Crete.
On combining the successful experimental results, it is found that : — (1) The subcutaneous injection of blood or serum withdrawn during the first twenty-four hours of the patient's illness caused fever 19 times. (2) Inoculation with the filtrate obtained by passing the diluted blood through a porcelain candle which retained the micrococcus melitensis, excited the disease 14 times. (3) Feeding experiments with infected sandflies were successful on 21 occasions.
This evidence is sufficient to shew that the fever is specific, and that it is caused by a filter-passing virus, which circulates in the blood during the first day of the illness, and that it is conveyed by the phlebotomus.
The movements of our soldiers and sailors have formed an experi- ment on a vast scale. Every year for the last century hundreds of susceptible subjects have been transported to localities where phlebotomi abound, and the number of cases of fever which have arisen after their exposure to the bites of these insects has been registered with great precision. We learn that a large proportion of our soldiers and sailors was attacked with this fever during their first summer of residence in phlebotomus-haunted places ; sometimes as many as 55 per cent, of the new arrivals have been seized.
On the other hand, the naval and military forces which have been despatched to tropical and sub-tropical parts where the sandfly does not exist have been exempt from this infection ; for instance, in Bernuida, of which the writer has personal knowledge, the phlebotomus is not found, but culex and stegomyia are abundant; "summer influenza" is unknown, although epidemics of dengue and yellow fever have broken out at rare intervals in times past.
When examined with the aid of a pocket lens, a phlebotomus is immediately recognised by its form and its very thick hairy coating.
