August 8, 1919] 



SCIENCE 



127 



ism? — The organism may be transmitted by 

 the insect by direct inoculation through the 

 proboscis, involving the active movement of 

 the parasite, or the passive transmission of 

 the parasite in the reflex actions which take 

 place in the sucking of blood. The organism 

 may be externally carried on the beak of the 

 insect and mechanically transmitted at the 

 time of sucking. It may be located in the 

 mouth parts of the insect and burrovr through 

 at the same time the insect is feeding. It 

 may be in a passive state on the insect and 

 become stimulated to attack the host when it 

 comes in contact with the warm body. The 

 organism may be regurgitated by the insect 

 on the body of its host and obtain entrance 

 by its own activity, or by being scratched in, 

 or by being licked up by the host. 



On the other hand, the organism may pass 

 through the insect, and pass out in its feces, 

 or in malpighian excretions. It may be 

 washed into the wound made by the sucking 

 of the insect, by fluids excreted at the time of 

 the feeding. It may remain in the feces on 

 the host and ultimately be scratched in or 

 licked up by the host. 



The organism may be taken up by the in- 

 sect and never normally pass out of the insect, 

 but be inoculated by the crushing of its in- 

 vertebrate host upon the body, and the scratch- 

 ing of infected portions of the insect's body 

 into the blood. 



Quite a series of disease organisms find 

 their way into the hosts because of the habit 

 of the host of feeding upon insects. 



6. What is the course of the organism in 

 the insect f — If the organism is taken up by 

 the insect in its larval stage, the organism 

 may pass directly through the larva and out 

 in its feces and may quite conceivably pass in 

 this manner through insect after insect larva 

 before it finally finds a vertebrate host. The 

 organism may be taken up by the larva and 

 remain dormant in some portion of the larva's 

 anatomy, or, on the other hand, it might 

 undergo considerable development and multi- 

 plication in the larva and remain there 

 through all the metamorphosis of the insect 

 until the latter arrives at maturity, at which 



time development of the organism may begin 

 or may continue. 



Upon being taken up in the blood by the 

 bite of the insect, the organism may lodge in 

 the cesophagus and carry out all its metamor- 

 phosis there, or in some of the organs of the 

 head and find its way into the salivary glands 

 and through the salivary secretions into a 

 new host. 



It may, on the other hand, pass back into 

 the gut, or into the stomach; from the stom- 

 ach its path may lead in many directions. It 

 may pass on in its course of development into 

 the rectum and out in the feces, or it may 

 enter the fatty bodies or pass into the gen- 

 eral cavity of the insect, or it may migrate 

 forward into the oesophagus and into the 

 labrum; and it may pass into the malpighian 

 tubules, or into the ovaries. 



The organism may enter the eggs and re- 

 main therein through their development into 

 the larviB or nymphs and be transmitted at 

 some stage of the development of the second 

 generation. 



7. What is the course of the organism on 

 leaving the insect? The organism may leave 

 the insect in the saliva and immediately enter 

 the blood puncture. It may bore tlirough the 

 labrima of the insect at the time of feeding 

 and enter the puncture. It may leave the 

 rectum of the insect on the malpighian glands 

 and be washed into the puncture by means 

 of the secretions of the coxal glands, or some 

 other excretions made at the time of feeding. 

 It may be excreted in malpighian secretions, 

 or rectal feces, or regurgitated in vomit, and 

 may lie dormant on the skin of the host, or 

 in the food of the host, imtil it is scratched 

 into the blood, or is taken into the mouth. 



On the other hand, it may be possible that 

 the organism requires another host after the 

 insect, and before it reaches its final host. 

 There are cases on record of the insect being 

 the first host, and two or three other animals 

 in succession being hosts of later stages. 



V. WHAT IS KNOWN ABOUT THE DISEASE TO BE 

 INVESTIGATED ? 



It is a primary essential that all the work- 

 ers be able to recognize the disease which they 



