i6 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



fluid are found: the nucleolus, a spherical corpuscle made \xpoipyrinm 

 to which the chromatin, a characteristic substance of the nucleus, fre- 

 quently attaches itself; the chromatic network, the thread of which is 

 made up of linm, a very slightly chromophilic substance, enclosing 

 some grains, the grains of chromatin, which possess a special afl&nity 

 for basic stains. The chromatin or nuclein is the most important 

 substance of the nucleus. 



Centriole. — In intimate contact with the exterior of the nucleus and 

 sometimes inside is usually foimd a small body called the centrosome, 

 or, if the dense chromatin alone is considered, the centriole (Fig. 20, 

 B, a). It is a small chromophilic grain which is often surrounded by a 

 clear zone of protoplasm caXLed-archoplasm. 



Fro. 2. Fig. 3. 



Fig. 2.T— Cells of Saccharomyces cerevisie. 



Fig. 3. — Cella made up of several energids; A, A portion of the mycelium, of a 

 mold, Aspergillus ochraceus. (After Dangeard.) B, Cell of an amceba, Pelomyxa 

 palustris {After Doflein). 



Value of the Nucleus. — The nucleus is an organ indispensable to 

 cellular life. It directs for the most part the physiological functions 

 of the cell. It plays an active part in nutrition as is indicated by the 

 fact that the greater part of the products of nutrition or of reserve 

 spreads itself around the nuclear membrane. Finally, it assumes an 

 important r61e in cellular division and in sexual phenomena. 



The experiments of Balbiani which have been repeated by other 

 authors show that the cell cannot function without its nucleus. By 

 cutting an infusorial cell in two portions, one of which contains the 

 nucleus and the other only its cytoplasm, Balbiani found that the 

 nucleated part was able to resist the wound which it had received 

 and regenerate the cytoplasm which was lacking; whereas the enucleated 

 portion soon perished. 



