50 Studies on the Neuroglia 



observers who have used differential neuroglia stains in their study of 

 this tissue agree in regarding the neuroglia fibers, not as cell processes, 

 since they are readily differentiated from the protoplasm of neuroglia 

 cells, from which they differ in chemical constitution and physical prop- 

 erties, as is shown by these staining methods, but as an intercellular 

 substance emancipated from the protoplasm of the neuroglia cells. 



One of the disadvantages of both the Weigert and Mallory neuroglia 

 stains is the fact that these stains can be used only on human tissue; 

 furthermore, owing to the fact that the neuroglia fibers break down 

 very readily, as was pointed out by Virchow many years ago, it is neces- 

 sary to have at one's disposal very fresh tissue in order to obtain satis- 

 factory staining of the neuroglia. Krause and Aguerr^, as has been 

 previously stated, were able by careful manipulation of the Weigert 

 method to obtain successful differential staining of the neuroglia in 

 apes and half-apes; this, however, is the only instance, so far as I have 

 been able to ascertain, in which a successful differential staining of the 

 neuroglia in vertebrates other than man has been obtained. Weigert 

 and Mallory both admit that their neuroglia staining methods are use- 

 ful only on fresh human tissue. The difficulty of obtaining very fresh 

 human tissue no doubt accounts for the fact that we have so few con- 

 firmatory observations of the views of Weigert and Mallory concerning 

 the structure of the neuroglia. The fact that it is often difficult to ob- 

 tain fresh human tissue and the further fact that these methods cannot 

 be used to stain the neuroglia of animals no doubt explains in part the 

 apparent hesitancy to accept their results in place of the results ob- 

 tained by the chrome-silver method, by means of which, as is well 

 known, neuroglia tissue may be stained in the central nervous system of 

 all vertebrates, whether embryonic or adult tissue is used. The reason 

 why the Weigert and Mallory stains are selective for human neuroglia 

 only is difficult to explain and must be ascribed to some slight difference 

 in the chemical composition of the neuroglia fibers of man and other 

 vertebrates, in which case we may look upon these staining methods as 

 so highly differential as to be applicable to the staining of human neu- 

 roglia only. In the hope that by modifying these methods a procedure 

 might be found by means of which the neuroglia of animals might be 

 stained, I spent much time in experimentation. All of my endeavors, 

 however, proved fruitless so long as I confined my attention to the 

 Weigert and Mallory methods. Much more satisfactory results were, 

 however, obtained after the writer became familiar with the Benda dif- 

 ferential neuroglia stain, published in September of last year. Benda 

 was led to continue his endeavors to discover a satisfactory stain for 



