MICEOOEGANISMS OF THE BODY 307 



diseases. Finally, certain deseases are transmitted usually 

 through the genito-urinary tract. Such, for example, are 

 certain of th^ venereal diseases, particularly gonorrhea and 

 syphilis in man and dourine in the horse. 



How Bacteria Leave the Body. — Inasmuch as most dis- 

 ease-producing bacteria do not multiply outside the body 

 of the man or animal in which they live or produce disease, 

 it is important to know the channels through which these 

 microorganisms may leave the body. In some cases the 

 organisms are found in the pus or exudates from the 

 wounds or surface lesions of the body. In other cases they 

 may be found in mucous secretions of the nose and respira- 

 tory tract, in still other cases in the saliva. The organism 

 causing diphtheria, for example, is usually present in the 

 throat and mouth. In many diseases the causal microorgan- 

 isms are excreted with the feces. This is particularly true 

 of the so-called intestinal diseases such as typhoid, para- 

 typhoid, Asiatic cholera and dysentery. Occasionally the 

 organisms may be excreted in the urine. This occurs occa- 

 sionally in typhoid fever. Insects are sometimes responsible 

 for withdrawal of organisms from the body when they suck 

 up the blood. This occurs in yellow fever, malaria and some 

 other diseases. 



Bacteria causing plant diseases frequently are not 

 released from the injured tissues until after the death and 

 disintegration of the tissue. In other cases exudates may 

 form and the organisms escape to surface. In still other 

 cases apparently the disease organism is transmitted by 

 sucking insects as in the curly leaf of the sugar beet. 



The Tjrpes of Diseases Produced by Microdrganisms. — 

 In the animal body the microorganisms sometimes invade 

 the blood stream, growing in the blood in all parts of the 

 body. Diseases of this type are termed bacteremias. A 

 bacteremia caused by entrance into the blood of an organism 

 usually responsible for pus production and inflammation 

 (such as Streptococcus or Staphylococcus) is frequently 



