ORGANIC CONSTITUENTS OF THE SCALES OF FISH. 
99 
rounded at the other. Intermixed were other more circular scales somewhat smaller 
and not pointed. They gave, after decalcitication, positive reactions for ichthylepidin. 
The “sucking disk” of the remora, when removed and treated in the same way as the 
integument, also gave strong positive reactions for ichthylepidin. This fact indicates 
that the substance may be present not only in scales, but also in highly specialized 
modifications of the fins. 
All the elasmobranch fishes examined gave negative results for ichthylepidin, as 
did also two teleosts, the sun-fish and puffer. The species investigated, with detailed 
analyses, are here given: 
34. Dog-fish (Mwtelus canis). 
35. Sand shark {Carcharias littoralis) . 
36. Dusky shark ( Carcharhinus obscurus). 
37. Bonnet skate {Raia erinacea). 
38. Sun-fish ( Mold mold ). 
39. Puffer (Spheroides maculatus) . 
The scales of the above-named species were isolated by means of caustic potash and 
then decalcified and tested. In no case was there any indication of loosely combined 
sulphur. Millon’s reagent, though it gave a slight reaction in most experiments, did 
not } T ield the characteristic rich ruby-red color given by the scales cited in the first 
list. The test indicates that these scales have an organic basis quite different from 
the others, as the following analyses will show: 
Dog-fish (Mustelus canis). — Portions of the integument of several specimens 
recently killed were freed from extraneous matter, so far as possible, then washed 
thoroughly and placed in 5 per cent caustic soda. After three days the connective 
tissue had dissolved and the minute scales were washed carefully by decantation. 
They were now extracted with 0.5 per cent HC1 for several days, the acid being 
frequently renewed. The washed, decalcified scales were now tested, as usual, with 
Millon’s reagent and lead-alkali. With the former there was a faint pink coloration; 
with the latter there was no blackening. About a gram of the decalcified scales was 
now boiled in a liter of water for some time, the water being renewed as it evaporated. 
After a few hours the liquid became yellowish, and gelatin was detected in solution 
by the usual tests; after boiling for 30 hours the scales had almost completely gone 
into solution, a very minute quantit}^ only remaining undissolved. The solution had 
the characteristics of a solution of gelatin, although it did not gelatinize, even after 
concentration. This was doubtless due to the long-continued boiling, which, as is 
well known, converts gelatin into its ungelatinizable form, B-glutin. The dog-fish 
scales thus seem to have only collogen as their organic basis, and to be quite free from 
ichthylepidin. 
Sand shark ( Carcharias littoralis). — The scales were isolated and treated as 
described above, except that the alkali extraction lasted five days. They behaved in 
every way like those of the dog-fish, and like them are free from ichthylepidin and 
have collogen as their organic basis. 
Dusky shark ( Carcharhinus obscurus). — The isolated scales reacted in every way 
like those of the dog-fish and sand shark. 
Bonnet skate {Raia erinacea). — The skin with scales, or rather spines, attached 
was removed from the caudal and posterior portions of the pectoral fins and treated 
with 5 per cent alkali (NaOH) as before. The star-shaped spines thus isolated were 
washed thoroughly, extracted several days with 0.5 per cent HC1 which was fre- 
quently changed. The residue was washed until the filtrate was free from chlorides. 
The scales gave no blackening with lead-alkali and only a faint pink color with 
