ITS CHEMICO-PHTSICAL AND MORPHOLOGICAL PROPERTIES 



55 



plasm, and hence the theory, more f ally described later, that the ) 

 blood discs of Mammals are not true cells, but only the products^ 

 of the metamorphosis, or of the development of former cells, may 

 be defended for many reasons. 



The only remaining instance of cells in which, on account of 

 their extreme minuteness, no differentiation into protoplasm and 

 nuclear substance can be demonstrated, is furnished by Bacteria 

 and other allied forms. However, even here Biitschli (II. 6) has 

 endeavoured to prove the existence of a nnclear-like body. Thus 

 in Oscillaria and in others (Fig 1 . 33 A, B), he has pointed out 

 bodies which are not digested by gastric juice, and which contain 

 a few granules, which stain intensely (probably nuclein granules) ; 

 these make up the greater part of 



the cell substance, the protoplasm B 



being present only as a delicate 

 envelope. Biitschli's views are for 

 the most part shared by Zacharias 

 (II. 47). 



Even if it is objected that the 

 above statement is at present nn- 

 proven, it cannot be denied that 

 the supposition that Bactei-ia con- 

 sist entirely, or principally, of nu- 

 clear substance, seems at any rate 

 as probable, if not more so, as the 

 one that they are minute masses 

 of pure protoplasm. The extra- 

 ordinary affinity of these organisms 

 for staining reagents is very much 

 in favour of the first view. 



IV. The Central or Pole Corpuscles of the Cell. Long 

 ago an exceedingly minute object, which, on account of its 

 function, is of the greatest importance, was observed in addition 

 to the nucleus in the protoplasm of some cells ; this is the central 

 or pole corpuscle (centrosome) . This was first noticed during cell 

 division (which is described later on in Chapter IV.), and here it 

 plays a most important part, as it forms a central point for the 

 peculiar radiated appearances, and above all functions as the centre 

 of the cell, around which the various cell contents are, to a certain 

 extent, arranged. 



As to size, it is only just visible, and is frequently much smaller 



m 



FIG. 33. A Otcillaria -. Optical section 

 of a cell from a thread, killed with 

 alcohol and stained with hsematoxylin 

 (after Butschli, Fig. 12 a). B Bacterium 

 Inieola (Cohn), in optical section, killed 

 with alcohol and stained with haema- 

 toxjlin (after Biitschli, Fig. 3 a). 



