f) We completed the studies of the effects of radiation upon fatty acids in vivo by considering them at the local tissue level. The first requirement was to establish a radiation procedure which would produce a standardized lesion. When radiations were applied directly to the skin of animals, the individual differences in response were quite marked. These could be explained in part on the basis of age and particularly of sex, the difference between the skin of male and female rats being manifest. However, there were also pronounced individual differences in animals of the same sex, age and weight living under the same conditions, so that even when the experimental procedure was carefully controlled, the same amount of radiation caused reactions that varied widely from slight erythema to ulceration.

The spectral analyses

Fig. 89. The spectral analyses (.01 in ethyl alcohol) of the fatty acids of the liver of a normal rat and of a rat irradiated 6 days previously with 1500r shows the appearance of the characteristic peaks of conjugated trienes.

Shows the spectral analyses

Fig. 90. Shows the spectral analyses (0.1 in ethyl alcohol) of the fatty acids of the lung of a normal rat and of a rat irradiated with 1500r 6 days previously. Peaks corresponding to conjugated trienes are present.

The problem of vaxiability was satisfactorily resolved by radiating abnormal tissues, such as those of a wound, instead of normal tissues. Standardized lesions were first produced and then irradiated. We used the following technique: an area of the skin on the back of male rats weighing around 200 grams was epilated and, under ether anaesthesia, a 2 cm. long incision was made, penetrating the skin and subcutaneous tissues down to the dorsal aponeurosis. A needle containing radium was then placed between the lips of the cutaneous wound. A thread passed through the hole at one end of the needle was used to fix it to the skin. Two retaining sutures were also used to maintain the radium needle between the lips of the wound. The needle was left in place for the desired length of time and then easily removed with the help of the thread passed through the hole of the needle. The retaining sutures were also removed and the wound left open and undressed.

Fatty acid conjugation and irradiation in vivo

Fig. 91. Fatty acid conjugation and irradiation in vivo. The changes in the oxalic index of total fatty acids of rats submitted to sublethal irradiation (600r.). Only a temporary increase in the oxalic index of the fatty acids of the animals is seen, the amounts not reaching the critical values.

The length of time that the needle was left in place varied with the amount of radium, the nature of the filtering metal, and the radiation burn desired. We found that 10 mg. of platinum filtered radium had to be left in place for about 90 hours in order to produce a standardized ulceration that would last about four weeks before healing. The same effect was obtained when 25 mg. of monel metal filtered radium was kept between the lips of the wound for only two hours. When monel metal needles were used for only one hour, too great differences appeared between the ulcerations obtained and the time necessary for their healing. A two hour exposure caused an ulceration which usually required 4 to 5 weeks to heal in control animals. If the needle was left in place for 3 hours, the ulcerations were quite uniform but they required over two months to heal and more than half of the wounds never healed. Failure to heal and more extensive necrosis resulted for periods of exposure beyond 3 hours.

Therefore, we utilized 10 mg. of radium in platinum for 90 hours in one group of experiments, and 25 mg. of radium in monel metal for 2 hours in another group, in order to produce standardized ulcerations that would generally heal spontaneously after 4 to 5 weeks. This technique has been used in several hundred animals for various experiments. The fatty acids of these standardized radiation lesions were studied.

Days after irradiation, the ulcerated lesions were removed along with about one cm. of surrounding tissue and submitted to analyses. It was always necessary to use as many as 5 or 6 lesions to obtain the quantity of fatty acids needed for an oxalic index determination. The lesions were found abnormally rich in conjugated fatty acids. Commonly, indices as high as 40—and in exceptional cases as high as 65—were found (Table XVI) in comparison with 0 or 0.3 for normal skin with its subcutaneous tissues.