Not only humans, but animals too shed tears when experiencing powerful pain excitations. Such a reaction of the lachrymal (tear producing) glands cannot be explained just by the function of the tears of protecting the eye; in the case of the lachrymal glands there must be admitted the existence of an also specific endocrine function, connected to the process of healing.
Experiments made on rats suggest this. Lab rats and Guinea pigs were removed skin patches from the back. In some experiments, researchers studied the scarring speed of the skin lesions under the influence of prolonged lachrymal glands excitation. For these purposes, the rodents were applied a heat source that led to slight burnings of the eye's cornea.
Because of the developing inflammation, the lachrymal glands produced a continuous and abundant secretion of tears. In the case of such an excitation of the lachrymal glands, the scarring rhythm of the skin lesions increased significantly, by 26-30 %, compared to the control group.
In other experiments, researchers removed the rats' and Guinea pigs' lachrymal glands and as a result the scarring of the lesions ocurred 6-8 days later than in the corresponding control group.
Interestingly, after the removal of the lachrymal glands, researchers noticed in rats an atonia (lack of muscular tonus), a decrease of skin elasticity and also a rapid and significant extension of the lesions' edges. It was obvious that the chemicals produced by the lachrymal glands participated in maintaining the normal tonus of the skin.
In other tests, researchers investigated the influence of a fluid extract obtained from the homogenate of lachrymal glands on the skin lesions on rats. A dose of the extract of 0.001 milligram per kilogram increased by 21.8 % the complete scarring speed of the lesions on rats with removed lachrymal glands, compared with control animals.
Thus, tears are more than an external advertising of pain; they heal the cause of the pain! At least of the physical one...