250 Journal of Comparative Neurology. 



sheaths, and in the sheaths or along them not infrequently 

 cells, the real significance and derivation of which is by no 

 means as clear as the term ' lymphoid-cells ' would make one 

 believe. Many ' lymphoid ' elements of the literature are 

 known to be neuroglia-cells. The satellite-cells, for instance, 

 cells grouped around nerve-cells and especially increased in 

 number in febrile and other processes, have repeatedly been 

 called leucocytes, lymphocytes, phagocytes and what not, while 

 it is fairly certain now that we are dealing with neuroglia-cells. 

 On the other hand the cells in the blood-vessel sheaths are most 

 frequently true cell-proliferations which are more properly de- 

 rived from vascular tissues, not 'lymphoid infiltrations.' Next 

 would come the various types of neuroglia and the nerve-cells. 

 That there are in the adult any cells of a non-determined char- 

 acter, such as Schaper mentions in his study of the genesis of 

 the elements of the nervous system, can hardly be doubtful, 

 but requires definite proof. A study of the neuroglia with 

 Mallory's or Weigert's method (or perhaps Robertson's ?) is ab- 

 solutely necessary for any valid statement on these structures, 

 and the numerous problems concerning the nerve-elements call 

 for methods for nuclei (Weigert, Heidenhain), for the Nissl- 

 bodies (Nissl), for the fibrils (progressive hasmatoxylin stain, 

 Graf, Bethe), the processes and their gemmules (Golgl), and 

 finally for the various states of the fibers (Weigert, Marchi, 

 Ehrlich, etc.) The composite picture of all these data will 

 give us an accurate idea of the histological composition of a 

 definite region. A sound pathological point of view demands 

 absolutely that we look upon the object in the first line as a 

 tissue. The general principles of nutrition and metabolism arc 

 only conceivable as related to a tissue, and only secondarily in 

 an analysis of cellular units. This is easily demonstrated. 

 The blood-supply is an all important index for the character oi 

 a tissue-type and on it depends the liability to special forms of 

 pathological derangements. In this sense the vascular arrange- 

 ment marks special forms of tissues. The other factor, closely 

 related to the vascularity is the specific life of the ' paren- 

 chyma, ' the nerve-elements. An interesting complication 



