This peculiarity was studied further under controlled conditions, using a radioactive 
form of Dipterexin rabbits.’ Again, whenthe rabbits were under stress, struggling against 
restraint, neither stableflies nor screwworms were destroyed. When doses ordinarily 
toxic for the rabbit were given, no symptoms appeared. 
G. W. Eddy of the ARS Corvallis, Oreg., Laboratory appeared to have encountered 
the same phenomenon in cattle treated for cattle grub control.* The cattle were chased 
deliberately before treatment by the cowboys to wear them down to a more tractable 
disposition. The cattle grub control was most unsatisfactory in this group. 
These casual observations of specific results of stress serve to warn us of possible 
additional effects. Toxicity studies are generally conducted with healthy animals, usually 
free of stress, and usually with the single operation of administering the compound 
being carried out. 
When the same material is given to sick animals, to those castrated, dehorned, 
vaccinated, and drenched in the same day, the results may be far different. It is not 
possible to predetermine all the possible combinations animal owners may devise; there- 
fore, we suggest that pesticide usage should follow or preceded such drastic stress by 
several days. 
Problems with Systemic Insecticides 
A new area of toxicology was opened by the development of systemically active com- 
pounds for plant and animal usage. The same problem existed for these materials as for 
the earlier ones, but new problems were added, Systemics were found to be changed within 
plants and animals to other related compounds, which might be more toxic to insects and 
livestock than the parent compound (81,102,103). Indeed, in most cases, some metabolic 
breakdown appeared necessary for the development of the systemic action. Careful study 
of this metabolism has givenus leads for new insecticides, more effective timing of treat- 
ment, and recognition of the limitations of the method. 
The study of pesticide toxicology has thus become a highly complicated science, re- 
quiring the services of several disciplines. It has not been sufficient to simply deter- 
mine a toxic dose for these materials. We have discussed the problems with those com- 
pounds on several occasions (91,93,100). 
The transformation of a chemical in plants or animals to substances other than the 
originally applied material (that is, schradan, thimet, and others) (13,23,76,117) compli- 
cates the evaluation of its potential hazard, particularly from the standpoint of residue in 
tissues, since we must not only evaluate the hazard of the compound applied, but of the 
new compounds derived from it. Additional complications occur because of the occasional 
unavailability of these derived compounds in sufficient quantity for animal experimenta- 
tion. 
The problem is not entirely limited to those materials considered to be systemically 
active. Aldrin and heptachlor are examples. These compounds, when absorbed by mam- 
mals, are biologically converted to their epoxides, dieldrin and heptachlor epoxide, and 
analyses must be performed for these compounds rather than aldrin or heptachlor. 
HERBICIDES 
The purpose of herbicides--killing of plants--limits the palatability of the treated 
vegetation in many cases, and reduces the period of attractiveness of the feeds to a very 
few weeks. The danger is primarily that of consuming the freshly treated plants. 
2 Unpublished results. 
3 Private communication, 
145 
