HOW PARASITIC AND PATHOGENIC BACTERIA REACH MAN 105 
the vagina. The gonococcus and Treponema palhdum are the more 
common pathogenic organisms whose portal of entry is the vagina. 
Uterus.— The normal uterns is sterile and the acid reaction of the 
vagina and the closure of the cervix uteri tends to maintain sterility 
under normal conditions. During menstruation and child-birth the 
mechanical defenses of the uterus are impaired. The organ itself 
appears to possess no specialized powers of resistance to infection. 
Urethra.— The urethra in health is practically free from bacteria. 
The flow of urine mechanically frees it from microbes. The external 
orifice of the urethra, however, frequently contains an acid-fast 
organism, B. smegmatis (which can be differentiated from the tubercle 
bacilli only by animal inoculation) and, very frequently, B. 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 infec- 
tion 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 
infection 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. Observations by Sweet and Stewart^ and by 
Eisendrath and Schultz^ suggest that infection of the bladder or lower 
ureter may reach even as high as the pelvis of the kidney through the 
interstitial lymphatics of the ureter. 
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 may 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 sus- 
ceptible to specific bacterial toxins as well as to the bacteria themselves. 
D. 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 con- 
plexity of the subject makes it difficult or even impossible to present 
in concrete form, a statement which shall indicate specifically the 
1 8urg., Gyuec. and Obst., 1914, 18, 460. 
■' Jour. Med. Res., 1917, 35, 295; Jour. Am. Med. Assn., 1917, 68, 540. 
3 It appears to be fairly well substantiated that cocci, especially staphylococci, have 
a tendency to invade the parenchymatous tissue of the kidney, whereas the colon-pVoteus 
group invades the pelvis and calices. 
