296 POPULAR SCIENCE MONTHLY. 



England or Scotland its origin has usually been traced to the " Emer- 

 ald Isle," where frequent epidemics have occurred during the present 

 century; that of 1826 to 1828 attained considerable proportions, and 

 that of 1846 to 1847 was the most severe of the present century. 

 The number of cases in the last-mentioned epidemic in Ireland i3 

 estimated to have been over a million, or about one in seven of the 

 population. 



Typhus has prevailed at various times in Mexico, Peru, and 

 Chili, as a result of importation from Spain, since the year 1570, 

 when it first appeared in Mexico. Its first introduction into the 

 United States was at a much later date, and corresponds with the 

 period of extensive emigration from Ireland to the United States 

 and Canada during the present century. For the most part the dis- 

 ease has been confined to the emigrants themselves, or to their imme- 

 diate attendants on board ship, at quarantine stations, or in the isola- 

 tion hospitals to which the sick have been transferred. Although 

 the disease has very frequently been brought to our seaport cities, 

 it has rarely extended to the resident population of these towns, 

 and is unknown in the interior of the country. In New York the 

 disease spread to some extent in 1818, 1827, 1837, and 1847, and in 

 Philadelphia a considerable epidemic occurred in 1836, and again 

 in 1862 to 1864. 



The conditions governing the epidemic prevalence of relapsing 

 fever are very similar to those mentioned in connection with the 

 aetiology of typhus. It is especially liable to prevail during times of 

 scarcity of food, and indeed epidemics are very frequently coin- 

 cident as to time and place with those of typhus. It is, no doubt, 

 transmitted by personal contagion, and its prevalence is therefore 

 largely influenced by circumstances relating to the susceptibility of 

 individuals, their sanitary surroundings, and their aggregation in 

 ill-ventilated apartments. It attacks more especially those individ- 

 uals in infected districts who occupy the densely populated and 

 filthy portions of towns and cities, and, as stated by Engel, is pecul- 

 iarly a morbus pauperum, or disease of the poor. On the other 

 hand, it is quite independent of climatic influences, and, so far as we 

 know, has no definite local habitat. The specific germ of this dis- 

 ease was discovered by the German physician Obermeier in 1873. 

 It is a slender spiral filament, endowed with very active movements, 

 and is found in the blood of relapsing-fever patients during the pri- 

 mary febrile paroxysm and also during the subsequent relapses 

 which are characteristic of the disease. 



It is impossible to say when or where relapsing fever had its 

 origin, but our first reliable accounts of the disease date from the 

 early part of the eighteenth century, when it prevailed as an epi- 



