CROUPOUS INFLAMMATION. 429 



in the highest magnifying powers. With one of Havtnack''s 

 immersion lenses, I have sneceeded in making out that the 

 ^'homogeneous" basement-membrane is not really homoo-ene- 

 ous, but perforated by a large number of very fine pores. 

 Through these pores the cells, of which there is usually a certain 

 quantity stored up between the basement-membrane and the 

 elastic layers, make their way to the surface. The apertures 

 indeed are small ; but is there any aperture so small as not to 

 allow the body of a young embryonic cell to slip through it ? 

 Those who, from personal observation, are familiar with the 

 amoeboid movements of these cells, will agree with me in answer- 

 ing this query in the negative ; they will also admit that the 

 "homogeneous" basement-membrane presents no obstacle to 

 their migration. 



§ 368. The presence of this basement-membrane underlies, 

 moreover, another important peculiarity of the croupous mem- 

 branes of the trachea, sc. that from the very first they adhere less 

 closely to the mucous surface than the false membranes of the 

 pharynx. Not only does the boundary-line between mucous 

 membrane and false membrane, between the secreting surface 

 and the secreted products remain clear and distinct throughout, 

 but the smoothness of the surface gives little chance of any 

 lasting union ever being brought about between the two. Con- 

 sider moreover the activity of the mucous follicles ; the free 

 escape of their secretions is often hindered by the superjacent 

 fiilse membrane, which they accordingly detach by accumulating 

 underneath it (fig. 124). The upshot of all these conditions is 

 the ease with which false membranes of the trachea may be 

 peeled off, a property on which all our therapeutic measures, 

 inadequate as they are, repose. Indeed the separation of the 

 false membrane not unfrequently proves the immediate cause of 

 death ; the membrane, wholly or partially detached, becoming 

 rolled up and completely blocking up the tube. The membranes 

 in tracheal croup may undergo softening as well as separation. 

 A gelatinous transformation of the network, together with a 

 flitty-granular disintegration of the embedded cells, arc the chief 

 factors in this process. Some observers have detected fungoid 

 vegetations in the softened pulp, and have accordingly ascribed 

 more of a putrid character to this liquefaction. The naked-eye 

 appearances justify us in calling it a true '' melting," inasmuch 



