NUCLEI. 29 



a dimly granular appearance, but no really granular struc- 

 ture, is the intercellular substance of the so-called hyaline car- 

 tilage. 



In the parts which present determinate structure, certain 

 primary forms may be distinguished, which, by their various 

 modifications and modes of combination make up the tissues 

 and organs of the body. Such are, 1. Granules or molecules, 

 the simplest and minutest of the primary forms. They are 

 particles of various sizes, from immeasurable minuteness to the 

 10,000th of an inch in diameter ; of various and generally un- 

 certain composition, but usually so affecting light transmitted 

 through them, that at different focal distances their centre, or 

 margin, or whole substance, appears black. From this char- 

 acter, as well as from their low specific gravity (for in micro- 

 scopic examinations they always appear lighter than water), 

 and from their solubility in ether when they can be favorably 

 tested, it is probable that most granules are formed of fatty or 

 oily matter ; or, since they do not coalesce as minute drops 

 of 'oil would, that they are particles of oil coated over with 

 albumen deposited on them from the fluid in which they float. 

 In any fluid that is not too viscid, they exhibit the phenome- 

 non of molecular motion, shaking and vibrating incessantly, 

 and sometimes moving through the fluid, probably, in great 

 measure, under the influence of external vibration. 



Granules may be either free, as in milk, chyle, milky serum, 

 yolk-substance, and most tissues containing cells with granules ; 

 or inclosed, as are the granules in nerve-corpuscles, gland-cells, 

 and epithelium-cells, the pigment granules in the pigmentum 

 nigrum and medullary substance of the hair ; or imbedded, as 

 are the granules of phosphate and carbonate of lime, in bones 

 and teeth. 



2. Nuclei, or cytoblasts (Fig. 1, 6), appear to be the simplest 

 elementary structures, next to granules. They were thus 

 named in accordance with the hypothesis that they are always 

 connected with cells, or tissues formed from cells, and that in 

 the development of these, each nucleus is the germ or centre 

 around which the cell is formed. The hypothesis is only par- 

 tially true, but the terms based on it are too familiarly ac- 

 cepted to make it advisable to change them till some more 

 exact and comprehensive theory is formed. 



Of the corpuscles called nuclei some are minute cellules or 

 vesicles, with walls formed of simple membrane, inclosing 

 often one or more particles, like minute granules, called nu- 

 cleoli (Fig, 1, c). Other nuclei, again, appear to be simply 

 small masses of protoplasm, with no trace of vesicular struc- 

 ture. 



