Figure 2. — X-ray photographs of larval fish 

 using Kodalith film. 



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species of young fish. We found, for 

 example, in making test exposures of small 

 mullet ( Mugil cephalus ) , approximately 18 

 mm. standard length, and a small pompano 

 ( Trachinotus carolinus ), 13 mn. standard 

 length, there was sufficient contrast be- 

 tween vertebrae to penrdt accurate deter- 

 minations in both species. The pompano 

 showed exceptionally good contrast, indi- 

 cating that acceptable radiograplis of even 

 smaller specimens could be made. 



CASSETTES 



A cassette is a paper or cardboard 

 envelope which holds the X-ray film, pro- 

 tecting it from exposure to unfiltered 

 light from the time it leaves the darkroom 

 \mtil returned for developing and fixing. 

 Various features, such as radiation filters 

 and intensifiers, may be incorported into 

 the construction of the cassette for special 

 radiograpnic purposes, but are not essen- 

 tial for routine examination of fish verte- 

 brae. Cardboard or paper of good quality 

 can be used with very satisfactory results. 



Commercial cardboard cassettes are 

 recommended for X-raying specimens larger 

 than approximately 55 inm. because of their 

 sturdy, lightproof construction. In smaller 

 specimens, horvever, the amount of radiation 

 absorbed or scattered by fibrous cardboard 

 becomes more critical. In such cases, a 

 thin, lightproof paper is suggested. In 

 either case, excessive fogging of the film 

 by secondary or reflected radiation may be 

 reduced by placing lead stripes between the 

 cassette and the X-ray table. 



DF7SL0Pi:i> AND FIXPIG 

 SOLUTIONS 



The following chemicals are necessary 

 for developing and fixing I-ray film: 



1. X-ray developer (two-pov; dor form) 



2. X-ray fixer (single powder) 



3. Acetic acid, 23 percent solution 



The developer and fixer solutions are pre- 

 pared according to directions given on the 

 labels of containers. 



I'igure 3. — Relation of exjDosure time to fish 

 using Kodalith film at 65 kv. 



