340 The Development of the Connective Tissues 



easier it is to isolate fibrils by digesting in pancreatin and bicarbonate 

 of soda. 



The action of pepsin and hydrochloric acid upon the connective-tissue 

 syncytium appears to be just the opposite of that of pancreatin. The 

 younger the syncytium the more ditticult it is to digest it in pepsin. 

 A section of a young embryo becomes opaque and shrinks a little when 

 placed in dilute hydrochloric acid and pepsin. It is shown by examin- 

 ing it with the microscope at this time that the nuclei are opaque, and 

 the white fibrous tissue, if present, has become transparent. After the 

 sections have been kept in the digestive fluid for a few hours at 37° C. 

 they still remain opaque and are somewhat elastic, for pressing a section 

 under a covergiass only spreads it but does not break it. When stained 

 with magenta the delicate fibrils of the syncytium are easily recognized. 

 When the sections are digested for 34 hours or longer they usually fall 

 into granules, showing that the syncytium is fully broken up. This is 

 especially the case if the sections are from embryos 10 cm. long or 

 longer. It is only in the smaller embryos that the syncytium is well 

 developed and in them we are to make the valuable tests. The sections 

 of an embryo 5 cm. long were still opaque at the end of 48 hours, with 

 considerable elasticity, indicating that the ' syncytium must be present 

 in considerable quantity. Furthermore, some fibrils could be seen from 

 time to time in bits of crushed sections. The cartilage and white 

 fibrous tissue of the perichordium resisted the action of the pepsin for 

 24 hours, but at the end of 48 hours they were fully dissolved. 



Sections of embryos hardened in alcohol can be easily digested upon 

 the glass slide and then stained with Mallory's connective-tissue stain 

 or with Weigert's elastic-tissue stain. If the digestion is continued 24 

 or 48 hours usually all of the connective tissue and syncytium are dis- 

 solved, leaving only broken cells to outline the structures of the 

 body. When the digestion is not complete it is found that usually 

 the white fibrous tissue is dissolved first, then the cartilage and then the 

 syncytium. A section through the body of an embryo, including the 

 umbilical cord, has in it from the ventral to the dorsal side all stages 

 of the syncytium in the process of differentiation. When such sections 

 are digested to a proper degree, usually from 24 to 36 hours, it is often 

 found that the white fibrous tissue of the body wall and back are dis- 

 solved while the syncytium of the cord is almost entirely intact; the 

 cartilages are destroyed only in part. 



It appears then that the connective-tissue syncytium is more resistant 

 towards the action of pepsin than is white fibrous tissue. The more 

 mucoid, that is, the younger, the syncytium is the more resistant it is 



