PARASITIC AND PATHOGENIC BACTERIA 105 



Urethra. The urethra in health is practically free from bacteria. 

 The flow of urine mechanically frees it from bacteria. The external 

 orifice of the urethra, however, frequently contains an acid-fast organ- 

 ism, Bacillus smegmatis, which can be differentiated from the tubercle 

 bacilli only by animal inoculation, and, very frequently, Bacillus coli. 

 The gonococcus and Treponema pallidum may invade the tissues 

 through the urethra. 



Urinary Bladder and Ureter. The slightly alkaline reaction of the 

 urine affords a good culture medium for many bacteria and infection 

 of the bladder by B. coli, B. proteus, B. typhosus and other micro- 

 organisms is by no means uncommon. It is probable that infection 

 occurs much more frequently through the blood or lymph than through 

 an ascending infection from the urethra. B. proteus appears to grow 

 with great luxuriance in the urinary bladder and a typical cystitis 

 may be readily incited in dogs by injecting virulent cultures of the 

 organism directly into the bladder. Occasionally a descending infec- 

 tion from an inflamed kidney may result in cystitis: whether a true 

 ascending infection through the ureter to the kidney takes place is 

 not definitely proven. 



Kidneys. The kidneys are normally free from bacteria, but infec- 

 tion of one or both kidneys through the blood stream is a well-estab- 

 lished phenomenon. A variety of organisms may thus infect the 

 kidney. The cocci of suppuration frequently incite acute nephritis 

 and tubercle bacilli induce chronic infection. Theoretically, any 

 invasive organism which enters the blood stream may localize in the 

 kidney and establish metastatic foci there. The organ is susceptible 

 to specific bacterial toxins as well as to the bacteria themselves. 



I). Where Bacteria Multiply in the Body. Practically no organ 

 or part of the body, except such structures as the nails, are free from 

 invasion with one or another kind of organism. The obvious com- 

 plexity of the subject makes it difficult or even impossible to present 

 in concrete form, a statement which shall indicate specifically the 

 types of organisms which incite infection in association with the 

 particular organs or tissues where they become localized. It is impor- 

 tant in this connection, however, to remember that a great majority 

 of progressively pathogenic bacteria exhibit rather marked affinities 

 for special tissues, and that they invade the tissues through definite 

 atria. The organisms which are habitually parasitic, on the contrary 

 the "opportunists" as Theobald Smith has so clearly pointed out, 

 are less exacting in this respect, as a rule, and they may invade the 



