viii PREFACE. 



lectures delivered at King's College Hospital. These 

 were published in the Medical Times and Gazette in 

 1871-72. 



The illustrations in the present volume are, I think, 

 in advance of any yet published by me. By printing 

 in three colours, very accurate copies of the specimens 

 prepared by the process of investigation I have long 

 adopted have been obtained. Although far less 

 beautiful than the preparations themselves, the figures 

 in the last few plates of this book really record with 

 accuracy the appearances observed. 



The method of preparing the specimens for exami- 

 nation under the highest magnifying powers is the 

 same that I have employed for many years past. 

 This has been described in detail in other works. 



From careful investigations, extending over many 

 years, I have been led to conclude that the particles 

 concerned in the propagation of contagious diseases 

 are allied in constitution to the living matter or bio- 

 plasm of the organism. The matter of which disease 

 germs consist is not, therefore, a non-living gaseous 

 liquid or solid substance, but the disease exciting 

 material is in an actually living state. I do not think 

 it is. derived from fungi or other low vegetable 



