Olfaction and Sharks — Tester 
161 
Fig. 8. View of a tiger shark attempting to swallow a spiny puffer. (Photograph by E. S. Hobson.) 
being tested as a potential shark repellent. With 
this substance, the greys responded violently 
with gill flexing, head shaking, and definite 
avoidance of the curtain. The tiger shark, on 
the other hand, was not noticeably affected until 
the concentration of the material had been dou- 
bled. 
In the foregoing sections it has been shown 
that certain species of sharks have an aversion 
to and at times are repelled by aged food ex- 
tracts, aged human blood, fresh or aged human 
sweat, and finally L-serine. Serine, presumably 
the D-isomer, is a common amino acid in both 
foodstuffs and blood. It may by hypothesized 
that at least one of the repelling substances in 
all of the above materials is L-serine, which is 
presumably present as the L-isomer in human 
sweat, but which may be formed in foodstuffs 
and blood from the nonrepellent D-isomer dur- 
ing decomposition. 
It has not been demonstrated that L-serine 
has sufficiently active repellent properties to 
deter shark attack on prey, including man. How- 
ever its repellent properties, its presence in hu- 
man sweat, and its possible generation during 
the decomposition of foodstuffs and blood war- 
rant further investigation. 
RESPONSE TO LIVING FISH 
Although at times sharks may obtain a large 
portion of their food by scavenging dead ma- 
terials, they also feed on living prey. When the 
prey is wounded, the sharks are doubtless at- 
tracted by the odor of body juices as well as 
by visual and possibly by other stimuli. It is 
