322 DR. E. KLEIN. 



(a.) For the nuclei of surface epithelial cells 0*0 IT by 

 0"00T millimetres. 



(b.) Nuclei of gland-cells 0017 by 0-014 mm. 



(c.) And the same numbers for those of endotliclial plates. 



There are several questions which sugfrcst themselves in 

 connection with the observations just detailed : First, as 

 regards the 'granules' or bright dots that present them- 

 selves in the intranuclear network, we have to ask what 

 their exact nature is? As has been mentioned already 

 previously, many of the bright dots or granules can be 

 distinctly recognised as due to optical transverse sections of 

 fibrils, these being either twisted or bent, or being altogether 

 placed vertically ; this is the view also expressed by Flcm- 

 ming (1. c, p. 698). But I have no doubt that in some 

 .nuclei the more irregularly shaped dots are due to a thicken- 

 ing of fibrils from place to place, the fibrils not being always 

 cylindrical, but some showing a perfectly irregular outline. 

 • It is clear from this that the more shrunk the intranuclear 

 network or the more twisted and convoluted the fibrils the 

 more does the nucleus present the appearance of being 

 'granular.' And it is, no doubt, owing to this condition 

 that in hardened specimens we are able to distinguish some- 

 times only a granular condition of the nucleus. Thus, for 

 instance, the 'granular' nuclei of epithelial cells, lymph- 

 cells, unstriped muscle-cells, muscle-corpuscles, &c., of 

 different organs in many animals, including man and mam- 

 mals, are due merely to a shrunken or convoluted condition 

 of the intranuclear network, or to the fibrils having a 

 dense arrangement, as I shall have occasion to show on a 

 future occasion. 



Tlie few ' granules ' that one also observes occasionally 

 in nuclei in a fresh condition are due to some of the fibrils 

 being pcen in optical transverse section, the fibrils them- 

 selves being not easily differentiable. A careful examina- 

 tion with a good lens and a good light shows the correctness 

 of this in most cases. Thus, for instance, the examination 

 of the nuclei of fresh epithelium of frog, toad, or newt, 

 the nuclei of fresh coloured blood-corpuscles of these animals, 

 especially of toad, with a Zeiss's F Lens or a Hartnack's 

 Immersion No. 10, reveals fibrils in the nucleus, and also 

 shows tliat the 'granules' are due to the twisted or bent 

 condition of them. 



Another point which deserves consideration is the so-called 

 nucleolus. It is well known tbat many nuclei of the nrost 

 different kinds of cells contain a very conspicuous, highly re- 



