OBSERVATIONS ON STRUCTURE OF CELLS ANO NUCLEI. 127 



iu my first paper, viz. 5 p. c. solution of cbromate of ammonia for twenty- 

 four hours, tiien washing in water, staining in picrocarmine, and mounting in 

 glycerin. 



The hardening reagents that yield good results are chromic 

 acid ^ — ^ per cent., especially the above mixture of chromic acid 

 and spirit, and to a certain degree also methylated spirit. 

 Bichromate of potash and Miiller's fluid, chloride of gold, and 

 even osmic acid, are not so good ; the cell-substance has a ten- 

 dency to swell up too much. But also when using the first- 

 named reagents it is necessary that the tissue should be fresh. 

 I have found that the lapse of only a few hours between death 

 and hardening is capable of spoiling the appearance to a con- 

 siderable extent. 



When epithelial cells of villi of small intestine of dog, cat, 

 or pig are examined in the perfectly fresh condition in serum, 

 the fibrillar nature, especially tlie longitudinal fibrils of the cell- 

 substance, comes out very distinctly, although the cell-substauce 

 appears as if uniformly granular ; careful focussing dissolves 

 this into its true nature, viz., being the expression of fibrils seen 

 in optical section. But when the epithelial cells begin to 

 undergo disintegrating changes, such as constantly happen some 

 little time after death, or after the application of pressure, or — 

 what is always the easiest and best means — after the addition of 

 distilled water, the fibrillar nature is lost, the network becoming 

 broken up into irregular unequal fragments ; and now the cell- 

 substance presents the appearance as if irregularly and coarsely 

 granular. I have repeated these observations so often with the 

 same result that I am inclined to think that when the substance 

 of the epithelial cells of villi appears uniformly " granular,^' these 

 granules are the optical sections of the fibrils of the mtracellular 

 netioorh, but when this substance appears to contain irregular, 

 i. e. unequal granules, this is most probably due to a disintegra- 

 tion of the intracellular network, or to the presence of fat-granules. 



The nucleus of these epithelial cells is oval, and possess within 

 its membrane a distinct network of fibrils similar to that de- 

 scribed in nuclei in my first paper. There is no nucleolus 

 present, but we see small bright dots in the nodes of the 

 network, amongst which we recognise occasionally one or two 

 somewhat larger than the rest. In my first paper I have stated that 

 the majority of the bright dots in the network of the nuclei of 

 cells in the newt are due merely to optical sections of the fibrils 

 of that network, and that the larger particles are local thickenings 

 of the fibrils, either natural or artificial, i.e. owing to the 

 shrivelling up of them. This same interpretation I. have to 

 apply also to the nuclei of the intestinal epithelium of mammals. 

 As, I mentioned in my first paper, Heitzmann describes in various 



