CHAPTER IV. 



UETHODS OF SPREAD OF DISEASE— IMMUNITY- 

 BACTERIAL TOXINS— SERO-THERAPY. 



Methods of spread of disease — Epidemics — Methods of bacterial action 

 — The antagonism of micro-organisms — Immunity — Hypotheses of 

 immunity — The exhaustion or pabulum, antidote or retention, and 

 acquired tolerance hypotheses — Methods of producing artificial 

 immunity — Metabolic products of the growth of pathogenic bacteria 

 — Ptomaines — Isolation of ptomaines — Toxalbumoses, bacterial 

 proteins — Sero-therapy — Eesearches of Behring, Kitasato, Tizzoni 

 and others on antitoxins — Defensive proteids or alexins — Prepara- 

 tion of diphtheria antitoxin — Preparation of the toxins — Immunisa- 

 tion of the animals — Standardisation and preparation of the serum 

 — Preparation of antitetanic, antistreptococcic, antivenomous and 

 other sera. 



Che Methods of Spread of Infection. — The principal methods 

 >f infection are : 



1. Pulmonary infection, the bacilli or spores being 

 nspired. 



2. Intestinal infection, the organisms being swallowed 

 vith food, water, or dust. 



3. Inoculation through a wounded or unwounded surface 

 »f the skin or mucous surface. 



4. Infection by contagion, fomites, etc., in which the 

 nanner of entrance of the virus into the body is not pre- 

 lisely understood. 



The more important diseases may be roughly classed 

 mder the above four headings as follows : 



