12 THE GERM THEORY OF DISEASE. 



the subject is DOW quite extensive, and is, for the most part, 

 scattered through works upon disease in general, more es- 

 pecially works on surgery. Very few books were written 

 especially on this branch of medicine until quite recently ; 

 and these generally dealt with some particular phase of the 

 subject, or with the very recent experimentation, giving little 

 or no account of preceding inquiries. Therefore it is very 

 difficult for one who takes up the subject now to gain a 

 comprehensive view of it as a whole. It will be my object 

 to supply such a view in a short and concise recital of the 

 thought, experiment and discussion, that has been most eifect- 

 ive in leading to our present knowledge, and most essential 

 to an understanding of the work now being done in this 

 field. 



FIRST TRACES. 



For many centuries these ideas consisted in vague con- 

 jectures, arrived at from the study of contagion an undefined 

 something that could pass from the sick to the well, and cause 

 disease. We find that Ulysses (Homer's Odyssy, Book XXII), 

 used sulphurous acid to destroy the odor and toxic products 

 of decomposition. 



Early in the history of Greece we find that men had 

 learned that certain localities were unhealthy. Their notion 

 seemed to be that something obnoxious to health was being 

 generated at these places; and we find them acting with 

 judgment in regard to the location of their hospitals and 

 important buildings. The physicians of antiquity observed 

 that, in epidemic diseases the then existing theories were in- 

 sufficient. They recognized that there was something extra- 

 ordinary to deal with. They spoke of a " constitutio pestilens " 

 and of a "genus epidemicus," but as to the nature of this 

 constitution of disease they had few clear ideas. 



Diodorus found an explanation of the cause of the Athenian 



