ii8 



HOWELL. [Vol. IV. 



in a number of pathological formations, tubercle, syphilis, etc. 

 In the second class, the cell contains not many, but one huge 

 nucleus, often bent or coiled upon itself, or imperfectly seg- 

 mented or notched so as to form a complicated structure. 



These have been described as giant cells with budding 

 nuclei (Bizzozero [2] ) ; but it seems to me that they are worthy 

 of a more distinctive name. I shall speak of them here- 

 after as megakaryocytes, or large nucleated giant cells, while 

 the first class might be named polykaryocytes, or multi- 

 nucleated giant cells. Some of the German histologists, espe- 

 cially Arnold (3), have held that transitional forms can be 

 found between the two classes, and look upon them therefore 

 as two stages in the life-history of a single cell. The first stage 

 is supposed to be the large nucleated form, and this by frag- 

 mentation passes into the multinucleated form. My observa- 

 tions upon the cat have led me to believe that we have here 

 two entirely different cells, probably with different functions, 

 and that what are described as transitional forms, which I have 

 also seen, though very rarely, are such only in appearance, and 

 can be accounted for more easily upon other grounds, possibly 

 as cells undergoing degenerative changes. 



In the cat the polykaryocytes are found in great numbers in 

 the developing bone of the foetus, and are usually seen in sec- 

 tions lying upon the spicules of bone while in process of forma- 

 tion. In extra-uterine life they can be found also, but only in 

 the marrow of the spongy bone, in the neighborhood of the 

 bony dissepiments. I have never met with them, in the cat, 

 lying in the mass of red marrow which fills up the interstices 

 of the spongy bone and forms solid plugs at the ends of the 

 medullary cavity of the long bones. It is well known, also (4), 

 that when pieces of sponge or other porous substances are 

 introduced into serous cavities, the leucocytes swarm into the 

 interstices of the foreign body, and in a short while multi- 

 nucleated giant cells are found lying upon the partitions, just 

 as in the bone they lie upon the bony spicules. 



Very many hypotheses have been made as to the origin of 

 these cells, the chief question being whether they are derived 

 from the growth of a single small cell or from the fusion of a 

 number of separate cells. It is not necessary for me to give 

 here any detailed account of the views that are held upon this 



