TRANSMISSION OF DISEASE 63 



have been known to transmit diphtheria, typhoid, scarlatina, 

 and other conditions. 



Insects transmit disease in two ways, mechanically and 

 specifically. Diseases like typhoid and tuberculosis may be 

 transmitted by flies, which soil themselves on excreta or 

 sputum and deposit the infective matter upon food or other 

 objects, which later get into the human body. Other diseases 

 probably to be credited in this category are plague and 

 diphtheria. 



In the other class of insect- born disease the transmission 

 can only take place by this means. Thus malaria is only 

 transmitted from the sick to the uninfected by the Anopheles 

 mosquito, sleeping sickness only by the tsetse fly, and yellow 

 fever only by the Aedes mosquito. In these insects there is a 

 development of the virus to such a degree that it can be 

 infective for an unprotected person, and for each disease this 

 so-called cycle of development is necessary for its further 

 propagation. None of the diseases demanding an insect for 

 its spread can be transmitted by one person to another by 

 the most intimate personal contact. . . 



It may be laid down as a law that with the exception of 

 the few infectious disorders only carried by insects, intimate 

 personal contact is the most prolific source of the spread of 

 disease. The objects before mentioned clothing, dishes, 

 books, utensils, and so forth called " fomites," were formerly ! 

 believed of considerable importance in transmitting disease, 

 but latterly more weight has been laid upon individuals as 

 carriers of viruses. This has come to pass because it has been 

 found that more persons contract disease after having come 

 in contact with persons than with objects from sick-rooms, 

 and for this reason much room and object disinfection has 

 been stopped. The writer still thinks that disinfection of a 

 room should be done before physical cleaning, because of the 

 possible ganger to the cleaners of such a room where the virus 

 may lurk in corners and cervices. 



