this internal "chemical factory,"'' on challenge 
by a foreign antigen, can produce not one but 
literally tens of thousands of different anti- 
bodies, each of which is tailormade for one 
purpose. Our skills at chemical synthesis in 
the laboratory have nowhere near reached 
this degree of perfection. However, encourag- 
ing progress is being made toward finding 
chemical means of attacking certain com- 
monly occurring enzymes (or chemical pre- 
cursor systems), where the mechanism of 
action is understood well enough to permit 
adaptation to specific problems of vertebrate 
control. For example, the anticoagulants 
(-4-hydroxycoumarins and the -1-3- 
indandiones) interfere with the synthesis of 
prothrombin in the blood, They are the out- 
growth of studies to discover the cause of 
"sweet clover disease,'' a hemorrhagic ail- 
ment in cattle. It was found that the cause of 
this disease was the anticoagulant dicoumarin. 
The initial objective of later work was to find 
more active anticoagulants to prevent post- 
operative blood clots in humans, Our present- 
day anticoagulant rodenticides are byproducts 
of this medical research. 
Most of the major chemical and pharma- 
ceutical companies conduct screening pro- 
grams to discover new pesticides. Thenumber 
of test organisms is necessarily limited to a 
few species. It is unusual to have the initial 
screening include more than one species of 
mammal, one species of bird, and one species 
of fish. Since the mammal is often an albino 
rat or mouse, we Can expect to find that most 
"specific'' rodenticides apply to this group. 
In the search for an antiinflammatory drug, 
scientists at the McNeil Laboratories used 
mice as the test species. Having found several 
promising compounds that the mouse tolerated 
fairly well (nontoxic), the study was extended 
to include the white rat for confirmation of 
the anti-inflammatory effect. Much to every- 
one's surprise, the drug proved highly lethal 
to rats, Intensive work with this laboratory 
animal revealed that the drug Norbormide 
resulted in irreversible constriction of the 
blood vessels. So specific is the action of this 
drug on the enzyme system in the Norway rat 
that the closely related roof rat requires five 
times the quantity, whereas the house mouse 
is not affected until dosages of 2,500 mg, per 
kilogram are reached. Best of all, the bene- 
32 
ficial species most likely to come into contact 
with baits placed for Norway rat control show 
no vasoconstriction from the drug. This list 
includes dogs, cats, sheep, hogs, cattle, 
chickens, ducks, turkeys, and some 15 other 
species. As might be expected, if the investi- 
gation is carried far enough with other species, 
a few show toxic response but at much higher 
levels than for the brown rat (rabbits, guinea 
pig, hamster, nutria). 
Red squill and antu are also unique because 
of their high toxicity to the Norway rat and 
wide margin of safety for other animals. The 
specificity of squill is due to emetic effects of 
the toxic agent. Unlike most mammals, the 
rat cannot regurgitate. In the case of antu, 
its high degree of specificity is due to a wide 
differential in toxicity to various species and 
even within species. The LDsg to Norway 
rats is 8 mg. per kilogram, whereas the LDsq 
to roof rats is 220 mg. per kilogram. 
These examples are but a few of the many 
kinds of selective effects that may be pro- 
duced by different chemicals. Our knowledge 
of those that are highly specific for rats is 
in large part due to the extensive use of labo- 
ratory rats in medical research, Their dis- 
covery illustrates the importance of using 
target species in screening programs if we 
are to find substances for use in the manage- 
ment of vertebrate populations. 
A start has been made during the past year 
to provide the chemical industry with guide- 
lines for conducting tests of candidate pesti- 
cides on several indicator species of fishes, 
birds, and mammals. The tests are in addi- 
tion to those routinely conducted to determine 
efficacy and safety to man and domestic ani- 
mals, Data from these studies will provide 
early clues as to whether a new compound is 
likely to be hazardous to wildlife species other 
than target organisms. In some cases, the data 
may also reveal potential utility for other 
purposes. 
A new avicide, known under the code desig- 
nation DRC-1339, shows considerable promise 
as a _ slow-acting oral toxicant for use in 
starling control. It is 300 to 500 times more 
toxic to starlings than to rats, indicating a 
wide margin of safety for mammals, DRC-1339 
illustrates another mode of action, in that it 
interferes with the oxygen-carrying capacity 
of hemoglobin and causes tissue suffocation 
