THE GEOLOGICAL PAEALLEL 19 



forms have undergone wide and progressive variations. I 

 know no more convincing demonstration of the truth of evolu- 

 tion than the wonderful series of fossils collected by Marsh at 

 the National History Museum in New York, showing the pro- 

 gressive stages from the four-toed Eohippus no bigger than a 

 mastiff, to the one-toed horse of historical time. Of late, I 

 believe, an equally instructive series of fossils, starting from a 

 small tapir-like ancestor leading up to the modern elephant, 

 has been obtained from Egypt, and has been housed at South 

 Kensington. Here is the point which I would emphasize : the 

 vast majority of fossils are remains of species and genera which 

 have passed away. 



Now what is true in respect to these fossils would seem to 

 obtain in respect to zymotic diseases and their causative agents. 

 Some extend back unaltered in their characters to the very 

 earliest periods : others appear and cause wide devastation for 

 a few generations, and then are known no more. It is difficult 

 to ascribe to faulty observation only the fact that many of the 

 plagues and epidemics of classical times are unrecognizable to-day : 

 the simpler and more sensible view to take is that many of them 

 were diseases which have died out. Nor are we without modern 

 instances to this effect. Of these the tritest is the " Sweating 

 sickness " (Sudor anglicus) which, first noted in England in the 

 autumn of 1485, led to a high mortality, affecting not so much 

 the poor and ill -fed, as those in comfortable circumstances. 

 It was an extraordinarily acute visitation, death ensuing often 

 in the course of a few hours : some are described as passing into 

 their death-agony while walking in the street, without time 

 being afforded for them to be shrived. It came in epidemic 

 form with heavy mortality, and spread rapidly. The attacks, 

 characterized by high fever, profuse sweating and little pain, 

 are described as lasting for twenty-four hours. Of this disease 

 there were outbreaks in 1485, 1507, 1517, 1528, and finally in 

 1551. Creighton, it is true, suggests that it was introduced 

 from the Continent by the rabble of mercenaries who came 

 over with Henry VII., that, in fact, it is the same disease as the 

 Picardy sweat. Unfortunately for this hypothesis there is no 

 evidence of the prior existence of such a disease in Picardy or 

 elsewhere on the Continent, and the Picardy sweat was not heard 

 of until two hundred and thirty years after the " Sudor anglicus " 



