TECHNIC. 303 



ganglion cells situated in the pancreas and others entering from 

 without. The nonmedullated nerve-fibers form plexuses surround- 

 ing the excretory ducts and end in periacinal networks. Fibrils 

 from the network about the alveoli were traced to the secretory 

 cells. A portion of the nonmedullated nerves in the pancreas form 

 perivascular plexuses. 



The development of the pancreas is peculiar in that the larger 

 portion, together with the duct of Santorini, originates from the 

 dorsal intestinal wall, and a smaller portion from the ductus chole- 

 dochus. The latter part, with its accessory pancreatic duct, fuses 

 with the former, after which there is a gradual retrogression of the 

 duct of Santorini, so that finally the entire secretion of the pancreas 

 almost invariably flows into the pancreatic or Wirsungian duct. 



TECHNIC 



The oral mucous membrane may be fixed with corrosive sublimate or 

 alcohol, stained in bulk, and examined in cross-section. If special 

 structures, such as glands, nerves, or the distribution of mitoses, are to be 

 examined, special methods must be adopted. 



Teeth. In order to obtain a general view of the structure of the 

 teeth, the latter must be macerated and ground as in the case of bone. 



The relations of the hard and soft parts in undecalcified teeth are 

 best studied by the use of Koch's petrifaction method. 



The teeth may also be examined in section, and when decalcified are 

 treated as bone. Hydrochloric acid, dilute chromic acid, and picric acid 

 dissolve the enamel prisms, their cement- substance being the first to 

 disappear (von Ebner, 91). 



The enamel of young teeth stains brown in a solution of chromic acid 

 or its salts, and blackens in osmic acid. In the enamel cells, globules are 

 seen, which are stained in osmic acid. If longitudinal sections of the 

 enamel be corroded with hydrochloric acid, the cruciform arrangement 

 of the enamel prisms is plainly seen. 



The fibrils of the dentin may be demonstrated by decalcifying a tooth 

 in the fluid recommended by von Ebner, the teeth of young individuals 

 being well adapted for this purpose. Occasionally carious teeth also 

 show the fibrils plainly. Corrosion with hydrochloric acid produces the 

 same result. 



The cementum, especially that part lacking in cells, contains a large 

 number of Sharpey's fibers. 



The development of the teeth is studied in the embryo ; the jaw-bone 

 is fixed, decalcified, and cut in serial sections. The most convenient 

 material is a sheep embryo, which can almost always be had from the 

 slaughter-house. 



Taste-buds. To study the taste-buds of the tongue and the rela- 

 tions which their constituent cells bear to each other, fixation in Flem- 

 ming's fluid is recommended. The orientation of the taste-buds must be 

 very carefully done, after which exactly longitudinal or transverse serial 

 sections are made (not thicker than 5 /,i) and stained with safranin- 

 gentian-violet. 



