In all cases, every piece of equipment is specially cleaned, scoured, and dried. The animal's udder is cleaned and dried. From inside the udder until the chemist completes his analysis there is no chance given for outside insecticides to contaminate the milk to be studied.

To determine the amounts of insecticides in animal tissue, two methods are used. Appropriate amounts may be taken of various tissues during autopsies after death from poisoning or following slaughter. Samples taken after slaughter may be expensive, because if the residues be large the meat is not sold for human consumption and must be destroyed. The method also involves the use of many animals.

In studies of autopsy samples from cattle and sheep, it was found that even when the insecticide residues reached several hundred parts per million in the fat there were less than 2 p. p. in. in muscle tissue. It was then decided that fat would be the tissue of choice for later analytical work. The values given in this paper are all for fat the amount of insecticide in a given cut of meat will be in proportion to the percentage of fat contained in that meat. The values we give, therefore, are actually the extremes that would be found under the conditions of treatment stated.

A biopsy technique was devised to eliminate waste of animals and to provide better data. Treated animals are cast, suitably anesthetized, and a 2-ounce sample of fat is then taken from the caul through an abdominal incision. The process is much like an appendectomy. The method allows samples to be taken before treatment as well as several times after, or during, treatment. It also allows us to make sure that there are no measurable deposits of insecticide within an animal at the end of an experiment. The method allows one animal to provide the data that six or seven did by the autopsy method. It also produces more valuable data. Observations on the behavior of treated animals also are of value.

The chlorinated hydrocarbons outwardly show their effect on an animal by various nervous disturbances. No two animals poisoned by a given insecticide will show exactly the same chain of symptoms, yet the symptoms are enough alike to enable one to identify them.

An affected animal will generally first become excitable and a little more alert to its surroundings. Twitches of various muscles soon follow, beginning usually at the head and going backward along the body. The twitches may increase in intensity until there are spasms and, finally, convulsions. In addition, the animal might assume abnormal attitudes, such as standing with the head between the forelegs and under the body, a sternal position with the hind legs in standing position, and persistent chewing movements. Occasionally the animal attacks any moving object. There is usually profuse salivation, rolling of the eyes, dribbling of urine, and bawling. The body temperature may climb to 114 F.

Some animals show none of these active symptoms; instead they are depressed and unaware of their surroundings. Some animals are alternately depressed and excited. Severity of symptoms is no index of the likelihood of death or survival. Death may occur an hour or several weeks after exposure. Most cases run their course within 72 hours.

Findings at autopsy are somewhat variable. Alone, they never are diagnostic of poisoning by these insecticides. There will usually be cyanosis (blue-colored skin and membranes), congestion, and small hemorrhages of various organs, most frequently on the heart. The lungs usually are congested, heavy, and dark in color, suggesting primary stages of pneumonia. Often an excess of fluid occurs in and around the brain and spinal cord.

If the animal was affected over a long period, the carcass may be thin and lacking in moisture. The liver and kidneys may show abnormal consistencies.

Microscopic lesions in animals dying quickly are few, other than those mentioned, as observable at autopsy. In prolonged cases, there are fatty changes in the liver and kidney, some degeneration in those organs, and degeneration in the brain. Otherwise, few if any significant changes can be seen.

We prevent untold numbers of deaths of livestock and costly economic losses by making these experiments before new materials are widely used. Some animals have to be sacrificed in carefully controlled experiments in order that safe methods may be worked out enabling the livestock grower to use the new chemicals for improved pest control.

R. D. RADELEFF, a veterinarian in the Bureau of Animal Industry, is stationed at Kerrville, Tex. He is a graduate of Schreiner Institute and the Agricultural and Mechanical College of Texas. Since 1947 he has engaged in work on the problems of insecticide toxicology.

R. C. BUSHLAND is in charge of the Kerrville laboratory of the Bureau of Entomology and Plant Quarantine. After studying at South Dakota State College and Kansas State College, he joined the Bureau in 1935. Most of his research has been on insecticides. At the Bureau's Orlando laboratory during the Second World War, he was one of the group who first investigated the chlorinated hydrocarbon insecticides to establish their value in the field of medical entomology.

H. V. CLABORN, a chemist of the Bureau of Entomology and Plant Quarantine, is also stationed at Kerrville. Since 1929 he has worked for the division of insecticide investigations, the research laboratories of the Bureau of Dairy Industry, and the Food and Drug Administration. He is a native of Arkansas and a graduate of George Washington University.

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