232 The Development of the Neuroglia 



vary greatly in bulk, and, evidently, in age. Whenever possible, attention 

 was paid to the thickness as well as the length of the specimens. 



Only one method was employed with the first three specimens of the 

 series. They were fixed in Carnoy's (Van Gehuchten's) fluid, and thin 

 paraffin sections were stained with hsematoxylin and counterstained 

 with Congo red, the latter being an excellent cytoplasmic st9,in and 

 having been previously found very efficient to bring out cell boundaries 

 when such are present. Pieces of the spinal cord of the remaining of 

 the series were prepared by the special neuroglia method of Benda, oo, 

 the procedure followed being that employed by Huber, oi. In addi- 

 tion, however, at various intervals in the series, pieces were prepared 

 as were those of the first three stages. Also Mallory's method for 

 white fibrous connective tissue, oi, was frequently employed. 



For purposes of comparison and control, the silver method was 

 applied to pieces from ten stages in the series. Beginning at 10 milli- 

 meters, the first six of these stages were in the identical order of the 

 series; the remaining were at greater intervals. I was unalile to get 

 the silver method to succeed with specimens below 10 millimeters in 

 length. Both the " rapid Golgi method " and the application of silver 

 to material preserved in formalin were used. After considerable 

 manipulation, a successful precipitation of the silver salt was obtained 

 in all the stages above 10 millimeters deemed necessary, and in the 

 younger of these especially the results were remarkably satisfactory. 



Pieces of the spinal cord from ten of the stages were also subjected 

 to the digestive action of pancreatin. The youngest of these meas- 

 ured 15 millimeters, the oldest fcetus was 28 centimeters, while the 

 last two were from the suckling pig and from the adult. Pieces of 

 adult human spinal cord were also subjected to the digestion experi- 

 ments. The procedure followed in these experiments was that given 

 by Flint, 02, which had previously proven highly successful with pieces 

 of other tissues. With the youngest specimens it was found necessary 

 to remove the one or two segments required in situ and digest with tlie 

 vertebral canal intact. Alone, tliey are so small and become so friable 

 that there is danger of losing them entire. Older than 20 centimeters, 

 if care be used, sections of the cord 2 to 3 millimeters in thickness may 

 be handled during digestion. 



In determining the period at which medullation liegins, osinic acid 

 was employed upon pieces taken from pigs between 14 and 25 centi- 

 meters. 



By the Benda neuroglia stain, the neuroglia fibers and the eliromatin 

 of the nuclei stain deep blue. In fact, these are the only structures 



