AVENUES OF EXIT OF INFECTIOUS AGENTS. 163 



now been supplied, with additional evidence that another 

 disease, filariasis, is conveyed in the same way. It is 

 quite probable that many communicable diseases whose 

 infectious agents are still a mystery may be transmitted 

 by suctorial insects — at least this is suspected — but 

 these are facts for future investigations to disclose. 



It is often as important to know the manner of trans- 

 mission of a disease as its cause, because this may supply 

 the only data for combating it. Just this much is the 

 sum of our knowledge of yellow fever, yet that it may 

 be controlled has been conclusively proven by Major 

 Gorgas of the U. S. Army, in Havana, Cuba, and by 

 officers of the U. S. Public Health and Marine-Hospital 

 Service, in Louisiana last year (1905). The yellow 

 fever commission appointed by the Surgeon- General 

 of the U. S. Army, the commission to which we owe 

 our knowledge of the transmission of yellow fever by 

 mosquitoes, after it had made the latter discovery, was 

 able also to eliminate every other avenue of exit for the 

 causative agent except the blood, and thus made clear 

 the futility of attempting to circumscribe the disease by 

 disinfection of secretions, fomites, etc. It further 

 showed that extermination of mosquitoes offers the only 

 solution of this sanitary problem, because in no other 

 way can this unknown virus get out of one patient's 

 body and into another. Therefore, when we say a 

 micro-organism makes its exit in the blood, it is under- 

 stood that this is accomplished through the bite of an 



