A CHAPTER ON INSECTS 137 



1. The particular organism producing the disease 

 is not known probably because it is too small for 

 microscopic observation. Nevertheless, it is demon- 

 strated that there is something in the blood that 

 produces the disease. This something is assumed to 

 be of animal nature owing to the requirement of 

 two hosts and a relatively long time to complete its 

 cycle. For want of a better name it is designated a 

 virus. 



2. The demonstration that it can not be trans- 

 mitted by clothing, bedding, contact with the sick 

 nor through the atmosphere. Prior to 1898 it was 

 generally believed that these were sources of infection 

 but two young privates of the United States army 

 John R. Kissinger and J. J. Moran volunteered to 

 put the question to a practical test, and for twenty 

 nights they slept in contact with bedding and night 

 clothing removed from those sick and dying with 

 yellow fever. No contagion followed and thus it was 

 proved that the disease can not be conveyed in this 

 manner. This service to the cause of science by these 

 two men involved great courage and high devotion to 

 the cause of humanity. 



3. Experimental evidence that, on the other 

 hand, yellow fever is transmitted by the bite of 



