ABILITY OF BACTERIA TO PRODUCE DISEASE 103 



The type of infection already described, with its period of incuba- 

 tion, symptoms, high fever, decline, and convalescence, is spoken 

 of as an acute infection. 



A third type characterized by a slow development and mild 

 symptoms and terminating after months or years either in death 

 or recovery is spoken of as a chronic infection. In these infections 

 it may be that the parasites develop and produce their toxins very 

 slowly or that they are only partially absorbed by the tissues. In 

 this way the body cells are only stimulated to produce sufficient 

 protective substances for their immediate need. Gradually, 

 however, the body cells may become exhausted and unless aroused 

 by some such means as the administration of a vaccine to produce 

 an oversupply of antibodies they may be slowly but surely over- 

 come. 



The Spread of Infection. The amount of infectious material 

 and the path by which it is discharged play perhaps the largest 

 role in the dissemination of disease. In diphtheria, typhoid fever, 

 cholera, influenza, gonorrhea, and pulmonary tuberculosis enormous 

 numbers of virulent bacteria leave the body in the discharges 

 from the mouth, nose, intestines, or genito-urinary tract. Con- 

 versely, in such diseases as streptococcic meningitis, gonorrhea! 

 rheumatism, and tuberculous peritonitis there is little danger of 

 infecting others because few or no living bacteria are 'discharged 

 from the body. 



The species of animals that may be infected has a slight influence 

 in the spread of disease. Anthrax, glanders, tuberculosis, hydro- 

 phobia, and some other diseases appear both in man and animals ; 

 certain other infections such as gonorrhea, syphilis, measles, 

 typhoid fever, etc., never, so far as is known, occur in animals, 

 and consequently are not transmitted by them. 



Another important factor is the resistance of the specific organ- 

 ism to conditions outside of the body. Spore-bearing bacteria, 

 such as anthrax and tetanus bacilli, will retain their pathogenic 

 powers for years. Certain non-spore-forming organisms, such as 

 those causing influenza, gonorrhea, and syphilis, are extremely 

 sensitive ; pneumococci and cholera spirilla are a little more resist- 



