INTRODUCTION 9 



matic. The ancient Greeks recognized the contagiousness of 

 several diseases and Galen classed plague, itch, ophthalmia, con- 

 sumption and rabies as contagious. Fracas torius (1546) during 

 the period of the great epidemic of syphilis in Europe, published 

 a book containing the first comprehensive discussion of the theory 

 of contagion. He recognized contagion by contact, by fomites 

 and at a distance. Soiled material of all kinds was included un- 

 der fomites, as also those healthy individuals capable of trans- 

 mitting disease, a phenomenon already recognized. Transmis- 

 sion by insects and animals was also included under this head. 

 The transmission "per distans" was considered due to emana- 

 tions from the patient diffusing to a distance through the 

 atmosphere. 



Kircher in 1658 claimed to have seen the living contagium in 

 the body in the form of minute worms, and his observations were 

 widely recognized. The objects he saw were not accurately 

 described but it seems very certain that they were not bacteria. 

 Probably they were the normal cells of the tissues. 



The discovery of bacteria by van Leeuwenhoek (1683) was 

 not immediately recognized as of importance for the germ 

 theory. Leeuwenhoek himself considered it impossible for his 

 "animalcula" to penetrate into the blood because of the com- 

 pactness of the epithelial tissues. 



Almost a century later, Plenciz (1762) maintained that each 

 infectious disease must have its own specific cause. Reimarus 

 (1794) also expressed the same opinion and considered these liv- 

 ing organisms to be of the order of infusoria or perhaps still 

 smaller beings not yet visible with the microscope. These ideas 

 were not supported by objective evidence and received only 

 passing attention. They were soon thrust aside by other inter- 

 esting if less valuable speculations. 



The development of general knowledge of the animalcules 

 in the early part of the nineteenth century, already referred to 

 in the discussion of the biological relationships and of fermentation, 

 was preparing the way for progress in the problem of disease. 



