SPECULATIONS UPON THE ORIGIN OF LIFE 639 



the Book of Genesis down to those advanced by Driesch, 

 Bergson and others. I therefore propose to leave vitalistie 

 ideas alone and to begin by glancing at certain pertinent points 

 relating to some properties of living matter which are common 

 to the overwhelming majority of organisms belonging to both the 

 animal and vegetable kingdoms. 



The unit of living matter, as far as we know, is the cell. I 

 will not at present try to give a comprehensive definition of a 

 cell but will deal, for the moment, only with that form in which 

 it is found in multicellular and the majority of unicellular 

 organisms both animal and vegetable. 



The cell, in this sense, is a mass of protoplasm generally so 

 small as to be invisible to the naked eye. In some cases it is 

 surrounded by a covering, which apparently may be formed 

 from a secretion or excretion and have ceased to be a living 

 part of the cell ; or it may be a membrane formed from the 

 protoplasm which continues to live. In other cases, the cell 

 is said to possess no covering but there are many observed 

 facts which make this assumption unacceptable. Whether 

 there is or is not always either a membranous covering or a 

 layer of differentiated protoplasm which acts as such is not 

 material to the point of view from which I am dealing with the 

 subject under discussion. 



Within the mass of protoplasm— the cell — is an area sur- 

 rounded by a membrane which differs in several ways from the 

 rest of the cell. This is the nucleus. The rest of the cell is 

 known as the cytoplasm. When cells are fixed and stained, it 

 is found that within the nucleus are collections of a substance 

 which has a great affinity for basic stains. On account of its 

 taking up stain very readily, this substance has been called 

 chromatin. Chromatin generally appears as minute granules, 

 sometimes collected together in masses of varying size, some- 

 times arranged in strings. The most usual form is a combination 

 of masses connected by a meshwork of strings. The chro- 

 matin appears to be always enclosed in an envelope of an 

 apparently homogeneous and not readily stainable substance 

 known as linin. 



Within the nucleus are usually found either a single or 

 several more or less rounded bodies, the nucleoli. These 

 generally differ to some extent from the chromatin in their 

 behaviour towards stains. 

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