MUCUS. 131 



former, that the colourless corpuscles are transformed into 

 red blood discs, nor with the latter, that every other cell met 

 with in the animal organism, proceeds from the white cor- 

 puscles of the blood. 



The white corpuscles of lymph, chyle, and blood I con- 

 ceive to be transformed into the epithelial cells, which con- 

 stitute the epithelium with which the internal surface of the 

 vessels of the entire vascular system is provided. 



The corpuscles of mucus I conceive to have an origin dis- 

 tinct from the colourless globules of the blood ; but in like 

 manner I regard them as elementary or tissue cells, believing 

 that they are finally developed into the different forms of 

 epithelium encountered upon the surface of mucous mem- 

 branes. 



The corpuscles of pus are also elementary cells, and mostly 

 altered mucous corpuscles. 



The view just expressed as to the nature of the white cor- 

 puscles of the blood, is one which has but recently impressed 

 itself upon my mind. It is not opposed, however, to the 

 opinion previously put forth of the connection existing be- 

 tween these corpuscles and nutrition, seeing that, whether in 

 their early stage of development as colourless blood globules, 

 or in the more mature condition of their growth as epithelial 

 scales, they are doubtless to be regarded as secreting organs, 

 and as effecting some important change in the constitution of 

 the liquor sanguinis. 



The only respect in which the opinion that the colourless 

 globules of the blood are converted into the scales which 

 constitute the lining epithelium of the vessels, is at variance 

 with a previously expressed view, is in relation to the escape 

 of those globules as an usual occurrence ; an opinion of Mr. 

 Addison, in which I was formerly disposed to concur, but 

 which I am now inclined to reject. 



A final^ reason which may be stated for disbelief in the 

 identity as regards the origin of the colourless corpuscles of 

 the blood and mucous globules, is the difficulty, not to say 

 impossibility, of explaining how these colourless corpuscles, 

 having precisely the same form and origin in the commence- 



M 



