128 ORGANISED FLUIDS. 



The form of the mucous corpuscle is also subject to alter- 

 ation from another cause, viz. pressure. Thus it is often seen 

 to be of an oval form in thick and tenacious mucus ; this 

 shape results from the pressure exercised upon the corpuscles 

 by the almost invisible fibres into which the fluid part of mucus 

 resolves itself, and which often become drawn out in the ad- 

 justment of the mucus on the port-object of the microscope. 

 (See Plate XII. ^.3.) 



The oval shape thus impressed upon it is permanent, be- 

 cause the pressure of the fibres of the solid mucus ceases not 

 to act: if the pressure however be direct, and the corpuscle 

 be immersed in a thinnish fluid, it will resume the spherical 

 form, the compressing force being removed, owing to the 

 elasticity with which it is endowed. 



Size. The size of the corpuscle is also liable to much 

 variation, this resulting mainly from the condition of the fluid 

 as to density, in which it is immersed. 



Thus, in water, or any other fluid, the density of which is 

 less considerable than that of its contents, the corpuscle im- 

 bibes by endosmosis the liquid by which it is surrounded, to 

 such an extent as to cause it to exceed by two or three times 

 its former dimensions. (See Plate XI. Jig. 3.) 



By reference then to the two particulars referred to, viz.. 

 the density of the medium in which it dwells, and pressure 

 we are enabled to explain all the varieties of form and size 

 which the mucous corpuscle presents. 



Properties. From the preceding remarks on the structure, 

 form, and size of the mucous corpuscle, we perceive that in all 

 these particulars, it accords closely with the white corpuscles 

 of the blood ; we shall now proceed to show that there are 

 other points of resemblance between the two organisms. 



Thus re-agents affect mucous corpuscles in a manner 

 precisely similar to that in which they act upon the white 

 globules of the blood; water causes them to increase in 

 size, acetic acid contracts them somewhat and renders the 

 nucleus and the molecules more distinct. Between mucous 

 corpuscles and the white globules of the blood there is, then, 

 a structural identity ; but let us see if there be not also a 

 functional correspondence. 



