562 FILTERABLE VIRUSES 



from a patient at this stage of the disease will reproduce the disease 

 in a non-immune. 



2. The virus will pass through a Berkefeld filter; it belongs, there- 

 fore, to the group of filterable viruses. Berkefeld filtrates of the 

 blood will establish the disease through a series of cases, thus indi- 

 cating that a living virus is being perpetuated. 



3. The disease is transmitted ordinarily by the bite of a female 

 mosquito belonging to the genus Aedes. The insect is now known as 

 Aedes calopus. 1 



4. A patient is infective for a mosquito only during the first seventy- 

 two hours after the initial chill and onset of the disease. 



5. A latent period, during which the insect is non-infectious, must 

 elapse before the disease may be transmitted to a non-immune subject 

 through the bite of the yellow fever mosquito. 



6. One attack appears to confer lasting immunity, provided the 

 individual resides continuously in the tropics. 



The two cardinal features of the transmission of yellow fever infec- 

 tivity of the patient during the first three days of the disease, and the 

 part played in its transmission by the mosquito, Aedes calopus, were 

 immediately put to the acid test of practical sanitation by Gorgas, 2 

 first in Havana and later in Panama, where he organized and directed 

 the sanitation of these pestilential cities along lines which soon freed 

 them from yellow fever and other diseases of endemic origin as well. 



The importance of the work of the American Yellow Fever Com- 

 mission and of Gorgas cannot be overestimated; the completion of 

 the Panama Canal and the liberation of the tropics from the dreaded 

 yellow fever mark a new era in Epidemiology and Preventive Medicine. 



Foot and Mouth Disease. 3 Foot and Mouth disease is an acute, 

 highly infectious exanthematous disease which attacks cloven-footed 

 animals chiefly. The characteristic eruptions, which are vesicular 

 at first and filled with a clear fluid, soon become grayish, and the 

 epidermis sloughs off, leaving a raw reddened surface. The eruption 

 usually appears at three distinct sites the mucous membrane of the 

 mouth, the teats, and interdigital spaces. The incubation period is 

 from one to six days, and little or no immunity to subsequent attacks 

 is conferred on an animal by successful recovery. 



1 The original name of the insect was Culex fasciatus; it has been changed succes- 

 sively to Stegomyia fasciata, Steogomyia calopus, and finally to Aedes calopus. 



2 See Jour. Am. Med. Assn., 1906, xlvi, 322, for brief summary. 



3 For an excellent discussion of various aspects of the disease, see the Cornell Vet., 

 February, 1915, Foot and Mouth Disease Number. 



