54 Studies on the Neuroglia 



For this investigation material was obtained from the following 

 vertebrates : 



Mammalia — Dog, cat, rabbit. 



Birds — Dove. 



Eeptilia — Tortoise (Emys meleagris). 



Amphibia — Frog (Eana Catesbiana and Kana halecina). 



It is my purpose at this time to give a brief descriptive statement 

 of observations made on the neuroglia of the spinal cord of the above- 

 mentioned vertebrates, differentially stained after Benda's method; 

 I shall deal only with the structure of the neuroglia tissue of adult 

 animals and not with its origin nor its distribution. A much more 

 extended treatment of this subject is contemplated and many of the 

 statements here made will then be substantiated by figures. This will 

 appear on the completion of work now in progress. 



Dog. In the dog, the neuroglia of the spinal cord consists of neu- 

 roglia cells and neuroglia fibers. With the method used, the nuclei of 

 the neuroglia cells stain a purplish-blue color the protoplasm a brown- 

 ish-red and the neuroglia fibers a deep blue. The nuclei of the neu- 

 roglia cells vary greatly in shape and structure, but may be described 

 under two general types with transition forms. The majority of the 

 neuroglia cell nuclei are vesicular with the chromatin arranged in fine 

 granules. The nuclei belonging to this type vary greatly in shape and 

 size. In the smaller varieties, which are generally of round or oval 

 shape, the chromatin is in the form of numerous small granules; in the 

 larger varieties, which are round, oval, or polymorphous, the chromatin 

 is found in the form of one or several granules, the nucleus being 

 otherwise homogeneous in appearance. The nuclei of the other type, 

 which are not numerous, stain diffusely and usually quite deeply and 

 are usually of round or oval shape and generally quite small. The 

 Benda method has the advantage of staining the protoplasm of the 

 neuroglia cells. The amount of protoplasm seen in connection with the 

 dift'erent neuroglia nuclei varies greatly. In connection with the small 

 vesicular nuclei with numerous chromatin granules, it is often difficult 

 to make out any protoplasm, many of them appearing as free nuclei; 

 now and then, however, a thin layer of protoplasm is made out, either 

 surrounding the whole nucleus or appearing at only one side of it. The 

 large vesicular nuclei with one or several larger chromatin granules are 

 usually associated with larger masses of protoplasm, in which case dis- 

 tinct neuroglia cells are distinguished. In cross sections of the spinal 

 cord, such cells present a variety of appearances, their shape depending 

 more or less on the space occupied; they may be triangular or quadran- 



