CH. II.] 



THE NUCLEUS 



similar tendency to coagulate under the influence of heat and other 

 agencies. (3) Lipoids. These are so called because they resemble 

 fats in their solubilities ; they are present usually only in small 

 quantities, and those which most constantly occur are phosphorised 

 fats (such as lecithin) and cholesterin, a monatomic alcohol. (4) In- 

 organic salts, especially phosphates and chlorides of calcium, sodium, 

 and potassium. 



The Nucleus. 



In form the nucleus is generally round or oval, but it may have 

 in some cases an irregular shape, and in other cases there may be 

 more than one nucleus in a cell. 



The nucleus exercises a controlling influence over the nutrition 

 and subdivision of the cell ; any portion of a cell cut off from the 

 nucleus undergoes degenerative changes. 



A nucleus consists of four parts 



1. The nuclear membrane, which encloses it. 



2. A network of fibres in appearance like the spongioplasm of the 



protoplasm, but on a larger scale ; that is to say, the threads 

 of which it is composed are much coarser and much more 

 readily seen. The name chromoplasm has been given to 

 this network. 



3. The nuclear sap or matrix, a semi-fluid and homogeneous 



substance which occupies the interstices of the spongework 

 of chromoplasm. 



4. Nucleoli ; these are of two principal varieties ; some are knots 



or thickened portions of the network (pseudo-nucleoli), and 

 others, the true nucleoli, lie in the nuclear sap. 



These four parts of the . nucleus are represented in tha next 

 diagram. 



Node of network 



Node of network 



k ~ Nuclear membrane. 

 Nucleolus. 



' Nuclear matrix. 



Nuclear network. 



FK;. G. The nucleus diagrammatic. (Waldeyer.) 



Iii the investigation of microscopic objects, a histologist is nearly 

 always obliged to use staining agents ; the extremely thin objects he 

 examines are so transparent that, without such stains, much of the 



