HEREDITY OF INSECT INFECTION. 75 



at 90 F. These findings also correspond with the 

 baeteriologic examination of the intestinal and 

 stomach contents. Verjbitski's work in relation 

 to the bedbug and plague was referred to above. 



Although plague is acute in both the animal 

 and insect hosts, maintenance is facilitated 

 through the large numbers of both hosts which 

 are present in plague centers. The conditions 

 render possible a more or less permanent source 

 of infection for the fleas through the continued 

 infection of fresh rats. The possibility also exists 

 that the chronic nodular plague of rats may be 

 subject to exacerbations, accompanied by septi- 

 cemic infection, a condition which would afford 

 opportunity for the further infection of fleas. It 

 has recently been shown by the work of Wherry 

 and others that the California ground-squirrels 

 have played a part in the persistence of plague in 

 that region, a discovery which may have profound 

 epidemiologic importance for the United States. 



Inheritance in the insect has been mentioned as 

 a factor in the maintenance of Texas fever, Af- 

 rican tick fever of man, yellow fever and Eocky 

 Mountain spotted fever. Schaudinn also found 

 that the mosquitoes which carry Trypanosoma noc- 

 tuce (the "halteridium" of the stone owl) pass the 

 micro-organisms to the next generation through 

 the eggs. In Texas fever this appears virtually to 

 be the sine qua non for maintenance in view of the 

 peculiar habit of the tick of going through its vari- 

 ous stages of development on the host to which 

 the larvae first become attached. 7 In order to make 



7. Most ticks pass through three active stages in their 

 development. The freshly engorged and impregnated female, 

 after a period of rest, lays a great many eggs. Following 

 an incubation period 6-legged larvae emerge from the eggs, and 



