102 INFECTION. 



organism at the same time. This is seen frequently in tuber- 

 culosis, pneumonia, wound infections, etc. A secondary in- 

 fection is one occurring in the course of another infection, 

 such as the streptococcus infections which occur in the course 

 of pulmonary tuberculosis. A terminal infection is one occur- 

 ring in an individual suffering from some chronic organic dis- 

 ease and which ends fatally. 



When the poison is generated within the body itself as the 

 result of faulty metabolism or inadequate elimination of waste 

 products and their subsequent decomposition, a form of poison- 

 ing occurs known as autointoxication, or autoinfection. This 

 form of poisoning should not be confused with poisoning by 

 alcohol, which also is defined as an intoxication. 



An. infectious disease is said to be contagious when the in- 

 fection is conveyed by fomites, as, for instance, the scales in 

 scarlet fever. All contagious diseases are infectious diseases 

 as well ; but all infectious diseases are not contagious. 

 Typhoid fever is a typical infectious disease. The two terms 

 are really synonymous, and yet there is a difference in the 

 method of conveyance of the disease. 



In an infectious disease the germ is the infecting medium, 

 and is carried from the sick to the well; whereas in a con- 

 tagious disease some medium, such as the scales in the exan- 

 thematous diseases, apparently carries the infection. A more 

 thorough study of the contagious diseases and the finding of 

 the exciting germ-cause may obviate the necessity of a divis- 

 ion into infectious and contagious diseases. 



The term miasmatic had reference to a disease due to a 

 " miasm," that is, noxious matter carried in the air. Malaria 

 was looked upon as the type of this class. The term is no 

 longer used since the method of infection has been deter- 

 mined. 



Although certain germs bear a causal relationship to dis- 

 ease, it is evident that the development of the disease, or the 

 manifestation of an infection, is dependent on many condi- 

 tions which influence the infection either one way or the other. 

 All the conditions favorable to the development and growth 

 of an organism must exist before disease will result. A 

 whole community may be exposed to the infection in its most 



