126 



SCIENCE 



[N. S. Vol. L. No. 1284 



III. PLAN OP OPERATION 



Before starting out on any lines of experi- 

 ment in this subject, there should be -written 

 down in concise form the facts already 

 gleaned on the practical problems of the the- 

 ories which have occurred to the various mem- 

 bers of the group. A clearly outlined course 

 of action should be made and be carefully 

 discussed and then the various steps in the 

 investigations thus outlined should be read 

 and modified to meet the changing views re- 

 sulting from the experiments. The course of 

 the work should always be kept plainly in 

 view. Each step should be rigorously and 

 skeptically scrutinized for defects. 



In as much as the investigation from this 

 point will consist of the answering by obser- 

 vation and experiment of a series of pointed 

 questions, I shall proceed with my discussion 

 in the form of queries. Probably many other 

 vital queries will occur to the reader, but it 

 is more than possible that he may overlook 

 some of these if not set forth here. When 

 each query is satisfactorily answered the prob- 

 lem is practically solved. 



IV. HOW CAN AN INSECT BE INVOLVED IN DISEASE 

 TRANSMISSION 



Insects^ may be involved in disease trans- 

 mission either by the transmission of an or- 

 ganism or the inoculation of a toxin or they 

 may be an intermediate phase in the life cycle 

 of an organism, but not come directly in con- 

 tact with the final host. 



1. What hind of organisms can insects 

 carry? — It has been demonstrated that insects 

 can carry bacteria, many types of protozoa 

 and many species of parasitic worms, and also 

 that certain species of insects may be instru- 

 mental in carrying eggs of other species of 

 insects which cause disease. 



2. In wliat manner may insect toxins bring 

 ahout disease? — Many species of insects bite, 

 and inoculate, at the time of the bite, a toxin 

 which may at times cause serious trouble. 



Some invertebrates inoculate the toxin by 



1 By insects, in this article, are meant those forms 

 of invertebrates popularly called insects, including 

 the Arthropoda. 



means of the mouth, some by means of a claw, 

 some by means of a caudal appendage, others 

 by means of the ovipositor. In some cases 

 the invertebrate penetrates the skin with its 

 mouth parts and as long as it is adhering, 

 toxins are created which may in certain cases 

 cause severe paralysis or death. The acci- 

 dental eating of certain insects in food will 

 cause poisoning because of the toxins con- 

 tained in the bodies of these insects. It is 

 believed, but not yet satisfactorily demon- 

 strated that the pollution of food by the ex- 

 creta of certain insects may cause certain 

 nutritional diseases. 



The presence of certain insects in the tis- 

 sues causes severe irritations and often the 

 formation of toxins. 



3. Can insects themselves cause disease? — 

 Many species of insects are known to live 

 parasitically upon the bodies of man and ani- 

 mals and by their constant sucking of blood 

 or gnawing, cause skin diseases. Other spe- 

 cies of insects habitually lay their eggs on 

 or in the flesh and breed commonly or ex- 

 clusively in living flesh, causing a destruc- 

 tion of the tissues. Many species of insects 

 are dependent upon mammalian blood for the 

 necessary nutriment to bring about reproduc- 

 tion. Some insect larvae are blood suckers. 

 It is not at all uncommon for insect larvse to 

 be ingested in food and for them to continue 

 their development in the intestines or other 

 organs, often at the expense of the tissues. 

 In some parts of the world insects are eaten 

 as food by the natives, sometimes in a raw 

 state, and it is not uncommon in such case 

 for the natives to be infected with parasitic 

 worms which pass their intermediate stages 

 in the bodies of these insects. 



4. Where may insects obtain the organisms 

 which cause disease? — Disease organisms may 

 be taken up by insects directly from the blood 

 of an infected host or they may be obtained 

 by sipping infected surfaces of the body or 

 taken up from the feces or other excretions 

 of an infected host. The insect may take up 

 the organisms from these excretions either in 

 its larval or its adult stage. 



5. Hoiv can the insect transmit the organ- 



