nervous tissue. Unfortunately, this indicator often fails because animals can die with 
high levels of the enzyme in the blood while others live quite normally with none in the 
blood. 
Carbamates.--Insecticides of this group are cholinesterase inhibitors but are 
generally not so active in this regard. Symptoms of poisoning generally parallel those 
produced by the organic phosphorus compounds, with a few additions. Usually the ataxia 
is more pronounced. The poisoned animal generally attempts to move rapidly, but suc- 
ceeds only in rolling end-over-end in a tumbling manner, recovers rapidly, and repeats 
the process. There is usually a great deal of trembling and shaking. The poisoning by 
carbamates follows the general course described for the organic phosphorus compounds, 
Lesions of Poisoning 
Chlorinated Hydrocarbons.--Acute poisoning by these compounds yields no pathog- 
mnomonic lesions. The lesions found are those expected in violent deaths from other 
causes--cloudy swelling, blanched viscera, and hemorrhages on various organs, In 
addition, there may occasionally be congestion of the lungs. The heart is generally found 
to be in systole. 
Subacute and chronic exposure lead to degenerative changes in the liver and kidneys. 
Organic Phosphorus Compounds and Carbamates.--This group usually leaves the 
viscera unmarked. Certainly there are no diagnostic lesions. Occasionally the lungs are 
edematous or congested, and occasionally there may be congestion with hemorrhages in 
various viscera. 
Herbicides.--The dinitro herbicides create severe damage in the kidneys and liver. 
The lungs are gray in color. Often there is a yellow discoloration of all tissues and fre- 
quently the odor of the compound is easily detected. 
The 2,-(2,4,5-trichlorophenoxy) propionic acid salts produce degenerative changes 
in the liver and kidneys and rather spectacular hemorrhages on the surface of the heart. 
The other phenoxy-acid compounds are reported to produce kidney and liver damage. 
Diagnosis of Poisoning 
Proper diagnosis of suspected poisoning of livestock has been a major concern of 
ARS. To aid in this problem, we have developed films describing and pointing out 
methods of arriving at correct diagnosis. 
Differential diagnosis was not, and is not, easyin the case of chlorinated hydrocarbon 
pesticides. The symptoms mimic those of many diseases in which the central or periph- 
eral nervous structures are afflicted. In many cases, a diagnosis can be reached only by 
eliminating all other possible conditions. Proper diagnosis are reached only after careful 
evaluation of the history of exposure, symptoms, and the lesions (the latter being non- 
pathognomonic in acute chlorinated hydrocarbon poisoning, but may suggest other disease 
processes), 
Differential diagnosis of poisoning by other pesticides is not appreciably easier. All 
must be approached with caution and carefully studied. 
Use of Cholinesterase Determinations in Diagnosis.--The organic phosphorus insec- 
ticides and the newer carbamates are recognized as inhibitors of cholinesterase, either 
as the original compound or as metabolites of the original. 
Originally, we (92), and others, felt that blood cholinesterase activity would be an 
excellent indicator of exposure and of poisoning. For single exposures we feel the method 
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