84 MICROSCOPICAL TECHNIQUE. 



results are obtained with melted carmine-gelatine, but it is import- 

 ant to keep the eye in hot water for half-an-hour before the injec- 

 tion is made and after the nozzle has been inserted, in order that 

 the gelatine may flow readily through the smallest vessels. It is 

 better to arrest the " bleeding " points, especially the veins, while 

 the injection is being made. He has generally found that it 

 requires as much pressure as could be exerted with one hand in 

 order to fill the vessels completely. The tension of the eye-ball 

 and the state of the conjunctive vessels serve as a guide to the 

 progress of the injection. Although carmine-gelatine gives very 

 good results, it does not afford a complete view of the vessels, 

 because the colouring matter in the capillaries is too small to pro- 

 duce any effect on the screen. To overcome this difficulty, I tried 

 an injection mass composed of gelatine and a preparation of 

 logwood, which gave excellent results. VVhen the injection is 

 complete, the eye must be cooled for a few hours in order to allow 

 the gelatine to set. The next stage consists in removing the entire 

 retina without tearing the membrane. This can best be done from 

 the front. The cornea is removed by making a cut with scissors 

 along its margin. Then the iris is removed in the same way, 

 taking care to wash off any pigment from the iris which remains, 

 since it is difficult to remove it from the retina if once it touches 

 that membrane. The lens is next removed by cutting through the 

 anterior part of the capsule, after which the vitreous, along with 

 the capsule of the lens, may be withdrawn from the eye by pulling 

 upon it with forceps, at the same time making pressure on the 

 posterior part of the sclerotic with the other hand. After the 

 removal of the vitreous, the retina will be found hanging down 

 from the optic disc, and its attachment there is to be divided with a 

 knife, sufficient room being allowed for the purpose by cutting away 

 part of the sclerotic. The retina may be freed and floated out in 

 water. With the aid of a soft camel-hair brush, the retina is now 

 spread on the glass, and it is important that no hardening agent, such 

 as alcohol, be used, since this has a tendency to cause unequal con- 

 traction of the gelatine. By carefully stretching the peripheral 

 parts, and slightly crowding together the central portions, it will be 

 found possible to adapt the whole retina to the flat surface of the 

 glass. Dehydration is carried out by slowly drying for twelve 



