^a INTRODUCTION 



men began to study the *' seats and causes" of disease, and tt^ 

 search out the changes inside the body, corresponding to the 

 outward symptoms and the external appearances. Morbid 

 anatomy began to be studied, and in the hundred years from 

 1750 to 1850 such colossal strides were made that we knew 

 well the post-mortem appearances of the more common 

 diseases; the recognition of which was greatly helped by a 

 study of the relation of the pathological appearances with the 

 signs and symptoms. The 19th century may be said to have 

 given us an extraordinarily full knowledge of the changes 

 which disease produces in the solids and fluids of the body. 

 Great advances, too, were made in the treatment of disease. 

 We learned to trust Nature more and drugs less; we got rid 

 (in part) of treatment by theory, and we ceased to have a 

 drug for every symptom. But much treatment was, and still 

 is, irrational, not based on a knowledge of the cause of the 

 disease. In a blundering way many important advances were 

 made, and even specifics were discovered — cinchona, for 

 example, had cured malaria for a hundred and fifty years 

 before Laveran found the cause. At the middle of the last 

 century we did not know much more of the actual causes of 

 the great scourges of the race, the plagues, the fevers and the 

 pestilences, than did the Greeks. Here comes in Pasteur's 

 great work. Before him Egyptian darkness; with his advent 

 a light that brightens more and more as the years give us ever 

 fuller knowledge. The facts that fevers were catching, that 

 epidemics spread, that infection could remain attached to 

 particles of clothing, etc., all gave support to the view that 

 the actual cause was something alive, a contagium vivum. It 

 was really a very old view, the germs of which may be found 

 in the Fathers, but which was first clearly expressed — so far 

 as I know — by Frascastorius, a Veronese physician in the 

 16th century, who spoke of the seeds of contagion passing from 

 one person to another; and he first drew a parallel between 

 the processes of contagion and the fermentation of wine. This 

 was more than one hundred years before Kircher, Leeuwen- 

 Hoek, and others, began to use the microscope and to see 



