60 



PIGMENTATION. 



phenomenon not only associated with the sudden death of the 

 blood-corpuscles, but serving also to usher in those changes 

 which, as in the present instance, lead rather to a gradual dis- 

 solution, or to a prolonged existence in another form. 



Note. — It is convenient to say a few words here about the conversion 

 of the colouring-matter of the blood into jDigment-granules without its 

 previous escape from the corpuscles. I allude to the so-called " blood- 

 corpuscle-holding cells." The mode of origin of these large, more or 

 less round, bodies, consisting of several red blood-corpuscles imbedded 

 in a colourless and homogeneous matrix (fig. 21a), was more important 

 formerly than it is now. It was thought to support the theory of endo- 

 genous cell-development. Its histogenetic interest has now quite faded. 

 It appears that these bodies are not always produced in the same 

 way. I have convinced myself that in the stagnant blood of amphibia 

 agglomerations of red and colourless blood-corpuscles (or such as have 

 become colourless), exhibit all the appearances of the " blood-corpuscle- 

 holding cells" (fig. 21&). 



Fig. 21. 



Blood-corpuscle-holding cells, a. Human ; 6. In frogs' 

 blood, ak- 



Preycr states (" On Amoeboid Blood- Corpuscles," Virclioio' sArchir, xxx. 

 417), that similar optical appearances may be produced by the escape of 

 the red contents of the corpuscles in stagnant frogs' blood in the form 

 of drops of varying dimensions, and the subsequent incorporation of 

 these drops into neighbouring amoeboid cells after the manner of par- 

 ticles of cinnabar, or other solid granules of any sort. This theory 

 admits of only a limited application to the " blood-corpuscle-holding 

 cells" of mammals, since in them the blood-corpuscles occupy a more 

 central position, and are enclosed on every side by a homogeneous 

 border. Here I believe that We have no alternative but to assume tliat 

 a layer of fibrin has been secondarily deposited round a group of blood- 

 corpuscles. The phenomenon would thus correspond on a very small 

 scale with that which recurs on a scale of ever-increasing greatness in 

 all circumscribed hemorrhages. The red blood-corpuscles go through 



