AND CONTENTS OF THE MOUTH. 309 



are kept back by the mucus wetting the larger air-tubes, where the 

 protecting barrier of the epithelia exists ; but they cannot reach 

 the slender bronchi or alveoli where the epithelium is evanescent 

 or at all wanting. Thus, the microbes, having reached the border 

 of the smallest bronchi, by means of the ciliary action, they are 

 thrust back towards the superior passages, and carried at last, by 

 the sputum, into the normal or pathological mucus. 



But if this happens in normal conditions, it cannot be so in 

 certain pathologic conditions, as in consumption, pleurisy, and 

 phthisis. The elements or parasitic germs, in these cases, not only 

 reach the most minute bronchi, but from there they diffuse them- 

 selves even to the remotest parts ; this may proceed from the 

 insufficiency of the ciliary action, or from an extraordinary con- 

 course of parasitic elements overcoming it, or from the microbes 

 along a denudated tract of mucous membrane. 



Forster and Graefe* were the first to write upon the vegetation 

 of filaments or branching threads of Leptothrix on the conjunc- 

 tival or lachrymal ducts ; Bizozzero draws a specimen in PI. V., 

 Fig. 52, of the quoted work. This has been reproduced in our 

 Fig. 6, d^ and it is natural to suppose that the relative germs origi- 

 nate from the nose. 



If now, from the buccal and nasal microbes, we pass to con- 

 sider those of the external genito-urinary passages, we shall find 

 the same disseminations ; but with this difference, that they will not 

 be found so frequently and in such abundance. This depends 

 upon two reasons : — The first is the relative scarcity of parasitic 

 vegetation, especially on the balano-preputial mucus (compared 

 with that of the mouth and nose together) ; the second is the 

 want of a propelling force, sufiiciently vigorous and repeated, 

 capable of pushing, at least in normal conditions, the elements or 

 the germs of the parasites in the urethra or in the bladder. At 

 any rate, we must admit a penetration, on a small scale, by looking 

 at the epithelia of the inferior urinary passages. Such epithelia, 

 even in the most normal and freshly-discharged urine, are found 

 impregnated with bacteria to such a degree that they cannot be 

 attributed to consecutive pollution (viz., after the urine has been 



* Forster, Arch, fur Ophtabii., t. xv., page 310. Graefe, Ueber Leptoth- 

 rix in den Thr<inenrohrchen,( Arch, cit., t. XVI., p. 324)* 



