CHAPTER V 



THE FROG: HISTOLOGY, THE GERM 

 CELLS, DEATH 



The study of tissues is a branch of anatomy known as 

 Histology. It was shown in the first chapter 

 c5to.' 08V thaX the tissues of the animal body consist of 

 protoplasm accompanied in many cases by a 

 ground-substance which supports it. The differences between 

 tissues depend upon differences in arrangement and com- 

 position both of the protoplasm and of the ground-substance. 

 When protoplasm is stained with certain dyes, a portion of 

 it colours more readily and deeply than the rest. This 

 portion is usually collected into minute masses known as 

 nuclei. The matter of which the nuclei are composed is 

 known as nucleoplasm, the rest of the protoplasm as cyto- 

 plasm. In most tissues 1 the protoplasm is arranged in the 

 little divisions, known as cells, to which we have already 

 alluded, each cell containing a nucleus and being of a size 

 and shape peculiar to the tissue to which it belongs. The 

 cells may either lie side by side (Fig. 5, C) or be separated 

 by ground-substance (Fig. 5, B) or by a space filled with 

 fluid (Fig. 63). Every cell arises by fission from another 

 cell, grows, and behaves to some extent as an independent 

 individual, but in the majority of cases it remains in 

 connection with its neighbours by fine strands of proto- 

 plasm. A cell - like unit with more than one nucleus 

 is known as a coznocyte, or sometimes as a multinucleate 

 cell. 



Either, as usually, in compact nuclei, or else scattered 

 through its substance, 2 protoplasm always contains nucleo- 



1 In all the tissues of the frog. 



2 In the latter case it is known as a chromidium. 



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