Irving Hardest}- • 259 



Tip to 16 centimeters the spinal cord digests out, leaving only a thin 

 cuff, the pia mater, with a fringe of delicate processes projecting from 

 its inner surface. These processes represent the walls of blood-vessels 

 and the ingrowths of the pia into the specimen. 



In pigs of 20 centimeters, digestion leaves results but slightly different 

 from the 16-centimeter stage. Though, as previously found, medulla- 

 tion is well underway at 20 centimeters and neuroglia fibers are begin- 

 ning to appear, it seems that there is not yet developed in the spinal cord 

 a framework sufficiently resistant to maintain even a delicate phantom 

 of the section. If the neuroglia fibers resist digestion, they must be 

 so few and dissociated that they are washed out in the process. The 

 cuff of pia is somewhat thicker than at 16 centimeters and its processes 

 into the cord are somewhat thicker and longer, but apparently none of 

 the framework of the developing medullary sheaths is maintained. 



At 28 centimeters the white substance has attained an evident resist- 

 ing framework, while the entire gray figure digests out practically clean. 

 The resulting opening in the transverse sections, giving a good outline 

 of the gray figure, is lined with a delicate fray of ingrowths. A narrow 

 space appears between the white substance and the pia mater, making it 

 seem as though the two are detached except for the blood-vessels and pial 

 ingrowths. 



The spinal cord of the suckling pig and of the adult behave much 

 alike when subjected to digestion. In the young relatively more sub- 

 stance is removed from the gray' figure than in the adult, and in the 

 latter, of course, all resistant structures are thicker and more closely 

 associated than in the young pig. 



In the adult spinal cord, both of the hog and human, a marked frame- 

 work resists digestion just as the connective-tissue framework of other 

 organs of the body does. It is well known that developed white fibrous 

 tissue resists the action of the pancreatin and, as first shown by Ewald 

 and Kiihne, 76, and by Eumpf, 78, the framework of the medullary 

 sheath resists digestion much as white fibrous tissue does. 



The intermixing of the white fibrous components of the spinal cord 

 with the neuroglia renders it difficult to determine the behavior of the 

 neuroglia in digestion. It can be said with certainty that all the proto- 

 plasm in the untransformed state, whether of ectodermal or mesodermal 

 origin, is removed by the action of the ferments, but it is not certain 

 with reference to the neuroglia fibers. The difficulty lies in the nature 

 of the digested preparations, and chiefly, perhaps, in the question of 

 staining. I have been unable to devise an application of the special 

 neuroglia stain which will differentiate neuroglia fibers in sections of the 



