FISHERY INDUSTRIES OF THE UNITED STATES, 1938 207 
parts per million of fluorine in the mackerel under similar conditions. 
These samples, supplemented only by vitamin concentrates, were fed 
as the diet of albino rats in the Bureau’s laboratories. No gross toxic 
effects were observed in any of the rats fed either species of fish during 
a test period of 12 weeks. However, an examination of the teeth of 
the experimental animals with a low power lens at the close of the test 
showed that the rats receiving the mackerel had developed fine white 
striations across the normal yellow of the enamel. None of the rats 
receiving the salmon showed any effects of striations and in no case 
was there any structural defect or abnormal growth of the teeth 
noted. 
Analyses of the carcasses of the rats showed a close correlation 
between the amount of flourine ingested in the food and the amount 
stored in the body of the rat. Whether the source of fluorine was 
mackerel or salmon, approximately 20 percent of the ingested fluorine 
was stored in the body of the animal in most cases. The average 
amount of fluorine in the bodies of the rats at the close of the test 
was slightly over 18 parts per million for the groups fed salmon, and 
about 74 parts per millon for those fed mackerel. The data show 
an inverse correlation between rat weight and the unit level of fluorine 
(in terms of parts per million). This was most marked where the 
variation in weight of the rats, within a group at the close of the 
test, was large. In other words, when the food intake and the rate 
of growth were below normal, a higher than normal percentage of the 
ingested fluorine was stored, and vice versa. These statistical or 
mathematical ratios, along with more detailed data, will be presented 
in a separate report to be published in the near future. However, 
it is well to point out here that, at the low levels of percentages of 
fluorine fed in the diet, a much higher percentage of the fluorine of 
inorganic origin added to the diet of the rat was stored in its body 
than was the case with the fluorine of inorganic origin. 
POSSIBLE TOXIC PROPERTIES OF CERTAIN FISH MEALS 
Fish meals, as now produced on a commercial scale in the United 
States, are manufactured under a great variety of conditions and, 
therefore, differ considerably in composition and quality. These 
variations are due to differences in chemical composition and relative 
freshness of the raw material from which the fish meal is made, dif- 
ferences in methods of manufacture and equipment used, and differ- 
ences in conditions of handling, storage, and shipment. Furthermore, 
fish scrap or meal was originally produced in this country primarily 
for use as an ingredient of commercial fertilizers, and it has only 
been in recent years that the major portion of it has been used as an 
ingredient of mixed feeds and of livestock rations. Therefore, the 
transition of the industry from the old methods of processing, suitable 
for a product of a fertilizer grade, to improved methods of manufac- 
ture necessary to produce feed concentrates of quality has naturally 
been a gradual one. Consequently, in a situation as described above, 
Federal and State regulatory feed officials and chemists have en- 
countered quite a problem in the equitable judging of quality of fish 
meals in connection with the administration of feed laws. Likewise, 
