Seasonal changes in organ weights and their relation to meteorological conditions.

Abstract

It is well known that many of the endocrine glands of normal animals undergo rhythmic changes in weight per unit of body weight which conform, in general, with seasonal conditions. Still, the cause of these changes is not clearly understood nor is it generally known that other organs and tissues such as the heart, the liver, the kidneys, the spleen, the thymus, the lymphoid tissues, and even the brain, undergo changes of a similar character.

In November, 1921, we began a series of investigations which included among other things a study of the ratio of the weights of various organs and tissues to the body weight of normal rabbits and the limits of variation that might be encountered, with especial reference to the causes of such variations. The factors studied included age, breed, length of caging, time of killing (with reference to the regular system of feeding), and meteorological conditions. All of the animals used were males, and an effort was made to minimize the influence of dietary factors by maintaining a uniform system of feeding and a uniform diet consisting of hay, oats, and cabbage, which is the regular diet given all rabbits in these laboratories.

The plan followed was to kill and examine two groups of rabbits each month selected from stocks that were being used for experimental work. All animals were well nourished and free from any external evidence of disease. During the first few months the groups were small and intentionally of a mixed character, but beginning with June, 1922, the monthly groups consisted of from ten to twenty rabbits.

The animals were killed prior to the daily feeding; they were anesthetized with ether and bled from the inferior vena cava while the heart was still beating. The organs were removed, freed of all adventitious material, and weighed on suitable balances.