PREFACE 



IT is the object of this atlas to present to students and teachers of histology a series 

 of photographs showing the appearance of the cells which form the central nervous system, 

 as seen under the microscope. These photographs have been made possible by the use of 

 the method of staining invented by Professor Camillo Golgi of Pavia. This method has 

 revealed many facts hitherto unknown, and has given a conception of the structure and con- 

 nections of the nerve cells both novel and important. In the light of these facts it has 

 been necessary to discard many of the views previously taught by anatomists, and to ' revise 

 some of the physiological and pathological data supposed to be fundamental. 



The nervous system is now known to be composed of a vast number of independent 

 units, called neurons, which consist of a cell body with two varieties of branches called den- 

 drites and neuraxons. The cell bodies vary in size, shape, and appearance ; their dendrites, 

 formerly known as protoplasmic processes, present great differences in form, length, and man- 

 ner of subdivision ; their neuraxons, formerly called axis cylinder processes and believed to 

 have no branches, are now known to give off many little collateral offshoots as important 

 as the main trunk. 



The arrangement of these neurons varies greatly in different parts of the nervous system. 

 In the spinal cord they are collected into groups arranged in a long cylindrical column. In 

 the cerebral axis they are scattered among the various nerve tracts as well as collected into 

 separate groups. In the basal ganglia they are gathered into large masses separable into 

 divisions. In the cortex of the cerebrum and cerebellum they are spread out into thin but 

 very extensive layers containing a great variety of cells. 



The interrelation of these neurons is also a subject of importance which recent researches 

 have demonstrated satisfactorily for the first time. The old theory that the processes of 

 adjacent cells joined together, forming everywhere a fine network of nerve fibres within the 

 gray matter, has been discarded. For the method of Golgi has shown that each cell is an 

 independent entity, its branches and subbranches of both varieties preserving their identity 

 from origin to ending, interlacing, it may be, with those of other cells, as the branches of 

 trees in a forest may interlace, but really as distinct and separable from each other as are 

 those trees with their twigs and leaves. 



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