Studies in Paleopathology 



3«3 



DISCUSSION OF GRAPH SHOWING INCREASE 

 OF DISEASE IN GEOLOGICAL TIME 



It is not necessary at this time to go into 

 further details concerning the progress of 

 disease, since the details are to be given in a 

 later paper. The accompanying graph (Fig. 

 6) will show how, according to present 

 evidences, disease has progressed during 

 the geological history of the earth. The 

 twenty-five divisions on the base line a-d 

 (,Fig. 6) represent as many periods of the 

 earth's history. The divisions on the vertical 

 line d-b represent the approximate number 

 of diseases present in each period, as indi- 

 cated by the known fossil lesions. The 

 time intervals in the graph are shown as of 

 equal value, but the geological periods are 

 not at all of equal duration nor of equal 

 character. This should be kept in mind in 

 studying the graph. 



At the point "a" we may say that organic 

 life is first known. It will be seen that the 

 line "a-b,' representing the history of dis- 

 ease, follows a base level for the first twelve 

 periods of the earth's history. Then the 



curve gradually rises until, during the 

 Cretaceous, at "c," diseases and accidents — 

 such as caries, osteoperiostitis, deforming 

 arthritides, necroses, hyperostosis, oste- 



Fig. 5. Callus and fracture in left radius of 

 Dimetrodon, a reptile from the Permian of Texas. 

 The specimen belongs to the Paleontological Col- 

 lections in Walker Museum, University of Chicago. 

 One-half natural size. 



Fig. 6. Graph showing increase of disease in 

 geological time. The d visions on the base line, 

 a-d, represent geo'ogical periods, and on the vertical 

 line prevalence of pathological condit ons. 



ophytes, osteomata, fractures — and many 

 infective processes, reached a maximum of 

 development among the dinosaurs, mosa- 

 saurs, crocodiles, plesiosaurs, and turtles. 

 The curve suddenly and sharply descends 

 from "c." For with the close of the Creta- 

 ceous and the sudden extinction of large 

 groups of the giant reptiles, the incidence of 

 disease also decreased. It seems quite prob- 

 able that many of the diseases which 

 afflicted the dinosaurs and their associates 

 became extinct with them. 



The mammals of the Cretaceous and 

 early Tertiary periods (Fig. 7) do not seem 

 to have been so generally afflicted with dis- 

 ease as were the preceding groups of giant 

 reptiles, nor as were the later mammals! 

 The ascending curve therefore is not so 

 abrupt as one might expect. Certain proc- 

 esses of disease seem to have been acquired 

 by the mammals from preceding forms, for 

 caries and other primitive diseases are evi- 

 dent (Fig. 8) among early Tertiary mam- 

 mals. The curve rises rapidly, however, and 

 reaches the highest point at "b," indicat- 

 ing that disease is much more prevalent 

 at the present time than ever before in the 

 history of the world. 



