BACTERIA IN DISEASE. 183 



tures in bouillon, makes infection more likely. Cultivation on 

 a particular medium may maintain or increase the virulence. 



Finally, the combination of two or more kinds of bacteria 

 may produce infection when neither one would do so alone. 

 On the other hand, it is said that the fatal effects of an inocula- 

 tion of virulent anthrax bacilli into a susceptible animal may 

 be averted if the animal be inoculated with a culture of bacillus 

 pyocyaneus shortly afterward. 



Mixed Infection. — It is not uncommon in disease to find 

 two kinds of bacteria associated together, producing a mixed 

 infection. In diphtheria, very frequently, the bacillus of 

 diphtheria is found to be accompanied in the membrane by the 

 streptococcus pyogenes. The course of the diphtheria may be 

 modified in this manner. The term secondary infection is 

 rather loosely used. It is sometimes employed to designate an 

 infection occurring in an individual, the resisting power of whose 

 tissues has been weakened by some chronic organic disease. 

 Such an infection is often called a terminal injection. Terminal 

 infections are very common in cases of carcinoma, chronic 

 nephritis, arteriosclerosis, and in many other diseases. 



Concerning terminal infections Osier says: "It mdy seem 

 paradoxical, but there is truth in the statement that persons 

 rarely die of the disease with which they suffer. Secondary 

 infections, or, as we are apt to call them in hospital work, 

 terminal infections, carry off many of the incurable cases in 

 the wards." 



The term secondary injection is also used for the modification 

 of an infectious process which has been in existence for some 

 time, by infection with a second species of bacteria. That 

 takes place, for instance, in pulmonary tuberculosis, when 

 the invasion of the already tuberculous lungs by the pyogenic 

 micrococci assist in the formation of cavities. In this sense 

 it will be seen that the term secondary infection is used as a 

 name for a variety of mixed infection. In the secondary. 



