Franklin P. Mall 355 



spindle-shaped masses of endoplasm. A faint Descement's membrane 

 is shown in specimens stained by Mallory's method; it does not stain 

 by Weigert's method. Practically the same condition is found in the 

 cornea of pigs 4 cm. long. 



In an embryo 6 cm. long the cornea has grown in thickness, the quan- 

 tity of exoplasm has increased and the nuclei have multiplied. The 

 general character of the exoplasm is as before. In the cornea of pigs 

 9 cm. long the adult condition is present, the lamellfe of the anterior 

 portion of the cornea being more developed than those of the posterior. 

 The exoplasm forms definite lamellae in the cornea of pigs 14 cm. long. 

 The fibrillated lamellae are bound together by bridges which run between 

 them. Descement's membrane is sharply defined, stains intensely blue 

 by Mallory's method, but does not stain by Weigert's method. It gives 

 the same reactions in the cornea of the adult. 



Xo elastic tissue can be demonstrated in the cornea of the adult 

 either by Weigert's method or by treating frozen sections with boiling 

 acetic acid and magenta. The lamellae of the cornea can be easily 

 resolved into fibrils by forming artificial cedema or by spreading frozen 

 sections. " In specimens made in this way the endoplasm is seen to 

 encircle the nuclei and forms an extensive syncytium, as is well known. 

 The tissue of the cornea contains much mucin and has often been 

 spoken of as an embryonic connective tissue. It appears to be tlje 

 only collagenous tissue which contains no accompanying elastic fibers. 

 In many respects the cornea resembles the perimysium of the embryo 

 before the white fibers have been fully formed from the exoplasm of 

 the syncytium. At this time there are also no elastic fibers in the 

 perimysium. 



Elastic Tissue. 



It is quite evident that in order to obtain any definite ideas regarding 

 the development of elastic tissue it must be studied when it first ap- 

 pears. Studying its extension when once formed may give results which 

 are misleading, for in older embryos the tissues which are being invaded 

 have also undergone development. 



In order to study the first appearance of elastic tissue I first tried to 

 follow it in the skin, both human and pig's, for here I obtained the best 

 preparations of developing white fibrous tissue. Furthermore, pieces 

 of skin are easily cut by the freezing method and treated with the 

 reagents usually employed in studying the connective-tissue fibrils. 

 Although numerous tests and specimens were made the results were 

 unsatisfactory until I had gained clearer pictures of the development 



