The embryos were removed from the uterus and immediately placed 

 into the killing fluid, which had been warmed to about body tempera- 

 ture. Smaller embryos were fixed in toto ; in larger specimens the 

 head was removed and sometimes cut longitudinally to permit uni- 

 form penetration. The material was left in the fluids at least 

 twenty-four hours. Dehydration was effected by means of alcohoi. 

 the material being passed through the usual grades of 25%, 35%, 

 etc., to absolute alcohol. It was then cleared in xylol or cedar oil, 

 the latter being preferred, because it clears readily from 95% alco- 

 hol and because it prevents the- tissues from becoming too brittle. 

 After being cleared, the tissue was embedded in paraffin. Sections 

 were cut in various thicknesses, 6, 8, 10, 15, and 25 microns. For 

 the study of the fibrous parts of the vitreous body, thick sections are 

 generally to be preferred. A number of sections were mounted 

 without the aid of a fixative to eliminate, as far as possible, all for- 

 eign material from the sections, a perfectly clean slide and careful 

 handling being necessary to bring about the desired results. The 

 fibers of the vitreous body are susceptible of almost all stains. 

 Good results were obtained with fuchsin, borax-carmine, Mallory's 

 connective tissue stain, Delafield's haematoxylin, Heidenhain's iron- 

 alum-haematoxylin with or without an additional slight stain of 

 eosin or erythrosin. Overstaining was resorted to in a few cases 

 to bring out the finer connections between the fibers. A heavy stain 

 greatly facilitates the study of this delicate tissue. No material 

 was stained in bulk, thus insuring a uniform stain. 



This method was found unsuited to embryos of more than 35 mm. 

 The action of the alcohol used in dehydration, and the heat neces- 

 sary for paraffin embedding caused greater or smaller shrinkage 

 of the vitreous fibers, while the subsequent removal of the paraffin 

 almost invariably led to a collapse of the delicate fibrous frame- 

 work of the vitreous body. For larger embryos a new method, first 

 described by Szent-Gyorgyi, with some modifications, was found to 

 give excellent results. 



As killing and fixing fluid the following mixture was used : 

 acetone 125 cc, formalin 40 cc, acetic acid 5 cc, water 100 cc, mer- 

 curic chloride 4 g. The eyes were carefully removed from their 

 sockets, freed of all adhering tissue, plunged into the killing fluid, 

 which had been heated to body temperature, and left in the fluid 

 from five to seven days, according to their size. Then to every 100 

 cc of the fluid 50 cc of concentrated acetone were added and the eyes 



