342 Obituary Notices of Fellows deceased. 



investigated by the experimental method, was new to those who 

 approached questions relating to the causation of disease from the 

 point of view of practical medicine. Simon's aim was to show that the 

 same methods which, during the preceding decade, had yielded such 

 remarkable fruits in physiology, could also be applied to the study of 

 disease; and that neither of these branches of knowledge presented 

 any exception to "the unbroken uniformity which prevails in the 

 operation of natural laws." 



The comparison of these lectures with Simon's later writings shows 

 us how, proceeding from the principle set forth in the words I have 

 quoted, he followed, during the 25 years of his active life, the rapid 

 progress of anatomical, clinical, and experimental discovery; taking 

 care not to be in front of ascertained fact, however far he might be in 

 advance of current teaching. From first to last, the side of pathology 

 which chiefly interested him was the aetiological, not merely because 

 the knowledge of the origin of a disease is indispensable for the under- 

 standing of its nature, but more directly in consideration of the 

 immediate practical value of such knowledge, as suggesting the means 

 of prevention. Among setiological questions, those of the specific 

 causes of infective diseases, and the manner in which they produce 

 their characteristic effects, were very fully considered in relation to the 

 doctrine of contagium. 



This now unfamiliar word was employed by Simon to designate the 

 material agent by which infection is communicated from the diseased 

 to the healthy body. In the lectures he attributed to "true 

 contagia " two characteristic endowments, namely, that they are able 

 to produce their characteristic results when given in the smallest 

 conceivable doses, and that " they undergo, in the body on which they 

 act, a striking and singular increase ; which increase, if recovered from, 

 confers on its subject immunity."* As to the way by which this 

 happens, he speculates as follows : a certain organic material A (the 

 contagium) enters into particular relations with B (a normal ingredient 

 of the blood). The effects of their coming together are (1) the utter 

 destruction of B, and (2) that A undergoes an immense augmentation. 

 " What has become of B 1 Whence has the new A been derived *? It 

 is difficult to avoid the conviction which arises with almost logical 

 certainty, that the increase of one material and the decrease of the 

 other have stood in an essential mutual relation ; that, in short, it has 

 been a process of conversion; that the essential relation of the two 

 matters (that derived from without, and that contained within the blood) 

 has consisted in the ready convertibility of the one into the other ; 

 that the specific power of the virus is its power of effecting this 

 transformation, and no other."! 



* Lecture XII., p. 258. f Lecture XII., p. 264. 



