120 



8 



more than ten times as many years. 

 Epidemics of Yellow fever, thanks to 

 those able and heroic American doctors, 

 are a thing of the past in civilised coun- 

 tries, and the name of Dr. Lazear, who 

 contracted the disease and died of it dur- 

 ing the enquiry, another of the numerous 

 martyrs whom science has claimed, will 

 always occupy an honored place in 

 the scroll of hygienic fame. 



I will not do more than give the outlines 

 of certain other work which has been car- 

 ried out in this direction. The recent 

 investigations which have been made into 

 Sleeping sickness — that strange disease 

 which overwhelms its victims with 

 an increasing languor and somnolence 

 until they perish of an apparent failure 

 of all the faculties— has received a 

 good deal of notice in the press. The 

 researches of Dr. Castellani, Dr. 

 Bruce, and others, go to show that the 

 conveying agent in this case is the Tsetse 

 fly, previously well known for the fatal 

 effects of its bite on horses and 

 cattle, but only lately known to be 

 connected with disease in human beings. 

 The mortality from Sleeping sickness in 

 certain parts of Africa has been alarming, 

 and whole districts have been decimated 

 by its ravages. The causative agent appears 

 to be a form of organism known as a try- 

 panosome, or, as it should be more cor- 

 retly termed, a herpetomonas, which 

 lives in the blood and fluids of the victim. 

 Further work yet requires to be done, 

 but little doubt remains that the curious 

 and fatal disease which almost invariably 

 kills its victim, and which has been 

 known as a scourge of Western Africa for 

 over 100 years, has been brought within 

 the grasp of science, and will be dealt with 

 as effectually as malaria and Yellow fever 

 are being dealt with. Whether the organ- 

 ism undergoes a part of its life history 

 within the Tsetse fly's body is not yet 

 definitely settled by actual observation, 

 but it seems probable that it does so. 



The presence of plague in Australia ren- 

 ders its causation and spread a matter of 

 perhaps more acute interest than the exotic 

 diseases with which I have been dealing. 

 The causative agent is, of cour«e, a well- 

 known bacillus, but the means whereby it 

 is habitually conveyed to human beings to 

 infect them have been widely discussed 

 amongst scientific men, and there is a 

 growing tendency on the part of those who 



have to deal with this disease to regard 

 more and more suspiciously a certain 

 insect which already possesses an evil 

 reputation in domestic sanitation ; I 

 allude to the flea. A good deal of work 

 has been done on these insects of late 

 years, and it may surprise you to learn 

 that more than 130 distinct species of flea 

 have been classified, and that new ones 

 are coming into knowledge month after 

 month. Eemarkable differences are 

 found in their structure and habits, 

 but in the particular connection with 

 which we have to consider them to- 

 night, one genus attains prominence — 

 the true pulices of which the type is the 

 human flea. 



Now, in considering the histories of 

 plague outbreaks in different parts of the 

 world, one is at once struck by a curious 

 fact, namely, that while preceding or 

 simultaneous outbreaks of the disease 

 amongst rats and other small rodents, 

 have formed a marked feature of plague 

 epidemics in the East, nothing of the 

 kind has attracted the attention of the 

 chroniclers of the European outbreaks of 

 the middle ages, and of the great plague 

 of London in 1665. The phenomenon is 

 striking enough to attract the attention of 

 any ordinary observer where it occurs, and 

 a significant allusion to it is to be found in 

 the First Book of Samuel. Other and even 

 more definite allusions occur scattered 

 through Eastern literature from a very 

 early date, so that it appears to have 

 attracted attention, and could scarcely 

 have escaped the acute chroniclers who 

 have left us such a vivid picture of 

 medieval and seventeenth century plague. 

 It is needless to remind you that the same 

 phenemenon occurs in Australia and in 

 South Africa at the present day. The 

 domestic rats of the East, of Australia, 

 and South Africa are very similar to those 

 of Europe, and all readily contract plague 

 when infected experimentally. But on 

 examination of their parasites a curious 

 fact was noticed in that the common rat 

 fleas of Australia, of India, and of South 

 Africa are widely different insects from 

 the common rat flea of Europe, both in 

 structure and habits. They are very 

 closely allied to the human flea, so 

 closely, in fact, that iheir relative identi- 

 fication is a matter of extreme difficulty, 

 without previous acquaintance with the 

 genus, and the Indian and Australian 



