200 SCIENCE PROGRESS 



to those already enumerated, which must be mentioned. This 

 is the part it plays in nutrition. The expression " resting 

 nucleus " is still to be found in the pages of many of our 

 text-books, though it is gradually being replaced by the more 

 appropriate term " non-dividing nucleus." For during life 

 there is no such thing as rest, and although the nucleus 

 may not be engaged in participating in the changes that lead 

 to cell division, it is doing something equally important. 

 However great may be the hiatuses in our knowledge of its 

 chemistry, this much at least is certain, namely that the 

 nucleus contains a store of nutritive material of a highly 

 complex nature, and the compounds contained therein consist 

 of carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, 

 iron and probably others in addition. This little barn or 

 storage-house is not one which keeps its doors locked, but 

 there is functional commerce between the nucleus and the 

 rest of the cell. If any part of a cell is separated from 

 the rest, and so cut off from communication with the nucleus, 

 that part rapidly degenerates and dies. A nerve fibre is 

 essentially just a long branch or tail of a nerve cell, and if 

 nerve fibres are severed, those portions of them which are thus 

 cut off from the nutritive control of the nucleus rapidly lose 

 their power to conduct nerve impulses, and the microscope 

 reveals in them those changes which are called after their 

 discoverer Wallerian degeneration. Wallerian degeneration 

 has been the subject of extended study because of its value 

 as an experimental method in tracking the course which nerve 

 fibres take, but after all it is but one example of a universal 

 truth. 



Staining reagents such as methylene blue, for which the 

 nucleus has a special affinity, also enable us to detect those 

 fragments of nuclear origin which have wandered out into 

 the cell body and its branches to satisfy the nutritional needs 

 and energy requirements of those parts ; these are particularly 

 well marked in nerve cells, and are known as Nissl's granules. 

 In the embryo, before the nerve cells have sprouted out any 

 branches, the nucleus is rich in this readily stainable material ; 

 but later on, when the branches have grown, its quantity is 

 lessened in the nucleus, for it has largely migrated into the 

 surrounding protoplasm. 



I shall not be anticipating too much what I hope to develop 



