RELAPSING FEVER. 655 



tension of the disease by contagion alone ; this is still more true of 

 the fact taught by experience, that, in places where relapsing fever 

 has not been seen for years, if a famine occur, and, from lack of proper 

 food, people are obliged to eat bad or spoiled provisions, the disease 

 will not unfrequently break out. On the other hand, there are grave 

 objections to this double mode of origin and extension. The same 

 reasons that satisfied us that the contagion in other infectious dis- 

 eases consists in low organisms, are just as valid in relapsing fever ; 

 and, although we cannot say it is impossible, we are still very averse 

 to supposing that organisms which reproduce themselves in the human 

 body may also develop and increase outside of it under such different 

 conditions. 



The great resemblance in the mode of extension of relapsing fever 

 and in its symptoms to the forms of typhus already treated of, cannot 

 escape notice. On the other hand, there are some points indicating a 

 difference between relapsing and typhus fevers, and a certain relation- 

 ship to intermittent fevers. This circumstance, as well as the fact 

 that there is no case known where a patient with typhoid or typhus 

 fever has communicated relapsing fever to another person, and vice 

 versa, has decided the best authorities to rank febris recurrens as 

 a third form of typhus after abdominal [typhoid] and exanthematic 

 [typhus] typhus fever. Now, if, after typhoid and typhus fevers had 

 long reigned, relapsing fever occurred with them or in their place, 

 this might probably be simply due to a modification of the low organ- 

 isms forming the contagion of typhoid or typhus fever, induced by the 

 vicinity of a marsh or the effect of bad food ; in other words, to the 

 development of a new species allied to but differing from the former 

 ones. 



I believe generally that the history of epidemics strongly supports 

 the correctness of JJarwirfs theory of the origin of new species. For 

 my part, I have no doubt that, in the course of centuries, new infec- 

 tious diseases have developed and taken the place of others that for- 

 merly prevailed. In the writings of the ancients we find wonderfully- 

 accurate descriptions, even of forms of disease, whose recognition and 

 distinction offered the greatest difficulties. There can be no doubt 

 that the regular and easily-recognized combination of symptoms char- 

 acterizing measles, scarlatina, typhoid fever, etc., would not have es- 

 caped the sharp observation of Sippocrates, if it had existed then as 

 it does now about the native place of the great Asklepiad.* 



If the correctness of this hypothesis be accepted, and the depen- 



* But in the writings of Hippocrates there is one place which seems to indicate 

 that febris recurrens occurred even in his day. 





