LIVING MATTEK 



13 



(&) The non-synchronous death of the several tissues or organs 

 of which the organism is composed. 



(c) The localisation of the effects of toxins and pathogenic 

 causes. 



(d) The possibility of transplanting and grafting tissues and 

 organs. 



(e) The possibility of multiplying not only plants, but also 

 many of the lower multicellular animals, for instance the fresh- 

 water Hydra by merotomy, or division into segments. 



II. The organisation of a perfect cell, capable of living and 

 reproducing itself, requires not merely a simple lump of proto- 

 plasm, as was originally maintained 

 by M. Schultze (1863) and subse- 

 quently by E. Haeckel (1870), but 

 the interior of the protoplasmic mass 

 must also contain a nucleus, a con- 

 stituent already described by previous 

 observers as an essential part of 

 elementary organisms. The later 

 work of Gruber (1888) on Ehizopoda 

 and of Biitschli (1890) on Bacteria, 

 has shown that these also consist of 

 two characteristically differentiated 

 parts, corresponding to the cell proto- 

 plasm or cytoplasm, and the nucleus 

 of the perfect cell. The membrane 

 which envelops the protoplasm cannot 

 be regarded as an essential part of 

 the cell, because while rarely absent 

 in plants, it is almost always lacking 

 in the animal cell. The centrosome 

 described by van Beneden and Boveri 

 (1887), and considered by them to 

 be the third element of the cell, 

 appears from the more recent work of Hertwig (1891) and 

 Brauer (1893) to be part of the nuclear substance, which is 

 generally extruded into the cytoplasm during the activity of the 

 nucleus, to incite germination and cell division. The morpho- 

 logical concept of the cell is accordingly very simple : it is funda- 

 mentally a lump of protoplasm which includes a more or less 

 distinct nucleus. 



The importance of the nucleus to the life of the cytoplasm can 

 be demonstrated experimentally, as also the importance of the 

 cytoplasm to the life of the nucleus. 



The first experiment consists in bisecting a unicellular animal, 

 e.g. an Amoeba (Fig. 1), in such a way that one half contains the 

 nucleus and the other is deprived of it : and then observing under 



FIG. 1. Amoeba protcus. (Hertwig.) M, 

 nucleus ; vc, contractile vacuole ; ?, 

 ingesta ; en, granular endoplasm or 

 granuloplasm ; ec, hyaline ectoplasm 

 or hyaloplasm. 



