278 J. S. FERGUSON 



The early studies of Kolliker, Ranvier and others, were largely 

 conducted upon teased and unstained reticulum or upon lymphoid 

 tissue from which the lymphocytes had been washed out by vari- 

 ous methods. They were followed by the employment of the 

 more recent dye reactions by which the recognition of the fibrillar 

 character of the tissue is rendered somewhat more apparent. It 

 was not until the more exact methods of chemistry and micro- 

 chemistry were applied by Siegfried, Mall and others that a fairly 

 clear perception of the exact structural relation of the reticular 

 tissue began to be apparent. The introduction of new methods 

 often renders plain certain hitherto obscure facts. This is espe- 

 cially true as a result of the silver impregnation methods of Biel- 

 schowsky ('04) w^hen applied to various connective tissues. Even 

 the finer fibers, which are more or less obscure after preparation 

 with other methods, stand out clearly in these preparations and 

 one is thus enabled to draw sharper distinctions than is otherwise 

 possible. It is with the application of this method, and its modi- 

 fication by Maresh ('05), that my observations were largely made; 

 the results have been confirmed by comparison with consecutive 

 serial sections stained by well known methods, chiefly depending 

 on haematoxylin and eosin, Mallory's fibroglia stain, and the 

 combination of haematoxylin with the Weigert and Van Giesen 

 stains described in my Textbook of Histology ('05). The tissues 

 studied have been lymphatic glands, spleen, tonsil, thymus, the 

 lymphoid tissues of the digestive and respiratory tracts, the skin 

 and various other tissues being used for comparison. The mate- 

 rial was obtained from man, pig, dog, cat, rabbit, ox, sheep, calf 

 and fish. It was fixed by the various methods in common use and 

 was both mature and embryonal. 



The method of impregnation which I have followed has been 

 a variation of the rapid modification described by Maresh ('05). 

 With individual exceptions I have gotten uniformly good results 

 after all the methods of fixation used. The method was applied 

 as follows: 



1. Sections cut in paraffin were fixed on the slide and placed 

 12 to 24 hours in a 2 per cent solution of silver nitrate. 



2. Transfer for 15 to 30 minutes to freshly prepared alkaline 

 silver solution (20 cc. of 2 per cent silver nitrate to which are added 



