56 



of typhus by Nicolle (1910) and by Wilder (1911), as the 

 distribution of these insects both in time and space does not 

 coincide with that of typhus. Wilder, however, tried experi- 

 mentally to convey the disease from monkey to monkey by 

 bugs, but without success. 



Verjbitski (1904) made a number of experiments on the 

 transmission of plague by the bed bug. He showed that 

 plague bacilli multiply in the stomach of bugs as they do in 

 that of fleas, and that their virulence was unimpaired. He 

 succeeded in conveying plague to guinea-pigs by the bites of 

 bugs, but only up to four days after they had fed on an 

 infected animal. 



There is really no evidence to incriminate the bed bug in 

 the case of either typhus or relapsing fever. It is possible 

 to transmit plague experimentally by means of bugs, but 

 there is no epidemiological reason for supposing this takes 

 place to any extent in nature. 



There are two differences in the habits of bugs and those 

 of fleas and lice which may possess epidemiological signifi- 

 cance. The first concerns the customary intervals between 

 their meals. Bugs show no disposition to feed for a day or 

 two after a full meal, whereas fleas and lice will suck blood 

 several times during the 24 hours. The second is in respect 

 to the time the insects retain a meal and the extent to which 

 it is digested before being excreted. Fleas and lice if con- 

 stantly fed freely empty their alimentary canals, and the 

 nature of their fasces indicates that the blood has undergone 

 but little digestion. 



Both these insects evacuate such undigested, or half 

 digested, blood per rectum during the act of feeding, and 

 the remnants of the previous meal are thus deposited in the 

 immediate vicinity of a fresh puncture. It is not unlikely 

 that, should the alimentary canal of the insect be infected 

 with plague bacilli, spirochaeta3,[pr the organism responsible 

 for typhus fever, these may be inoculated by rubbing or 

 scratching. Bugs have not this habit, and in all the cases I 

 have examined their dejections were fully digested, almost 

 free from protein, and consisted mostly of alkaline hasmatin. 



This is, however, probably not the whole explanation, and 

 . there is, I believe, much yet to learn as to the mechanisms 

 of insect transmission, and why one blood-sucking parasite 

 is an effective porter and another not, even in the cases of 

 bacterial infection where no stage in the life cycles of the 

 organism takes place within the insect host. 



