144 Lectures on Bacteria. [^ xiii. 



the more strictly mechanical effects of the parasite are of course 

 not impossible. 



XIII. 



Causal connection of parasitic Bacteria with infectious 

 diseases, especially in warm-blooaed animals. Intro- 

 duction, Relapsing fever. Tuberculosis. Gonorrhoea. 

 Cholera. Traumatic infectious diseases. Erysipelas. 

 Trachoma. Pneumonia. Leprosy. Syphilis. Cattle- 

 plague. Malaria. Typhoid fever. Diphtheria. In- 

 fectious diseases in which the presence of conta- 

 gium vivum has not been demonstrated. 



I. I SHOULD have wished to have added to the foregoing 

 two examples of facultative parasites which cause disease, one 

 example at least of a strictly obligate parasite, but I am unable 

 to find even one which is sufiBciently well known to allow a 

 detailed account to be given of it. All that can be produced on 

 this point will therefore be included in the following summary, 

 which is intended to contain in a few words the most important 

 part of the knowledge which we at present possess of the nature 

 of Bacteria as the exciting causes of infectious diseases in warm- 

 blooded animals, and especially in man (58). 



By the term infectious diseases we mean all those forms of 

 disease which are only found where they are conveyed from a 

 sick person to a healthy one so far as the particular disease is 

 concerned, or the origin of which is confined to localities of a 

 particular character. The former kind are known as contagious 

 diseases, such as scarlet fever, measles, small-pox ; the latter, of 

 which malarial fever is the best known example, are termed 

 miasmatic diseases. If the two conditions are combined, we may 

 speak of miasmo-contagious disease and that in two senses ; we 

 may mean firstly that a disease may be caught in certain localities, 

 or by infection from person to person independently of locality 

 of miasmatic character, or secondly that a disease is indeed 



