174 CONNECTIVE TISSUE. 



cement-substance cannot be distinguished from the other components of the 

 cornea. (See Fig. 65.) 



Further, I tried to stain the cornea of the dog and of the cat with chloride 

 of gold. Many experiments failed, though I had exposed the cornea to the 

 influence of the chloride of gold for hours. The after-treatment with acetic 

 and tartaric acid gave only negative results. I could never see distinct 

 cornea corpuscles with their ramifications until, at last, by the aid of lactic 

 acid, I succeeded in obtaining specimens of such beauty and clearness, that 

 all doubt with regard to the finest structure of the cornea disappeared. 



My method is the following : The cornea of a cat is taken out immediately 

 after death, soaked in a ten per cent, solution of lactic acid for a period of 

 about twelve hours ; then during one or two hours it is kept in a one-half per 

 cent, solution of chloride of gold, slightly acidulated by the addition of a few 

 drops of lactic acid, and finally exposed to the influence of daylight. The 

 superficial strata of the cornea and a peripheral border of one mm. turn yellow, 



FIG. 66. LAMELLA OF THE CORNEA OF A CAT, Two YEARS OLD, SOAKED 

 IN DILUTED LACTIC ACID AND THEN STAINED WITH A ONE-HALF PER 

 CENT. SOLUTION OF CHLORIDE OF GOLD. [PUBLISHED IN 1878.] 



P, dark violet fields, the cornea corpuscles, the nuclei of which are mostly hidden, with 

 offshoots of different sizes. The cornea corpuscles and their offshoots are connected with a 

 dark violet net- work traversing the pale violet basis-substance B ; the latter net- work shows 

 broader meshes than that of the corpuscles and their branches. Magnified 1000 diameters. 



and are of no use for examination, but the other part, the characteristic 

 purplish tint of which shines through the yellow envelope, is invaluable for 

 research. After having made the above described experiments, I learned 

 that F. S. W. Arnold, of New York, had previously used lactic acid for 

 the reduction of chloride of gold ; but he informed me that his method differs 

 from mine, inasmuch as he uses the chloride of gold in the first stage of the 

 preparation, followed by the lactic acid just the reverse of my plan of 

 treatment. 



