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ALTHOUGH the literature is replete with studies of the concentrations and in terrelations of the hormones during the physiological state of pregnancy in A. JV the mare, investigationsinvolving similar studies during the various phases of the estrous cycle of the non′pregnant mare are rare. Zondek (I) reported comparative data upon the estrogenic hormones in the urine of the pregnant and non-pregnant mare, and more recently Cole and Goss (2) cited the presence of gonad tropic hormone in the blood of the latter. However, nowhere in the literature are studies available upon the estrogens of the urine or follicular fluid in relation to the various phenomena of the estrual cycle. For periods beginning in February or April and ending about the middle of July of the years 1937,1938, and 1939 detailed studies were made in the physiology of the non-pregnant mare at the United States Range Live-Stock Experiment Station, Miles City, Montana.

Conclusions1. At sperm concentrations from 1 to 6 billion cells per cc an increase in concentration was accompanied by a decrease in sperm respiration rate. At concentrations of 0.2 to 1 billion sperm per cc this effect of concentration was not invariably observed. 2. In contrast with the behavior of sperm cells, respiration rates of yeast cells remained constant at concentrations from 1 to 8 billion cells per cc. 3. The effect of sperm concentration on sperm respiration rate does not appear to be due to changes in pH, diminished supply of O2 to individual cells, an enzyme, or products of metabolism. 4. When comparisons are to be made of relative respiration rates of semen samples, the samples must be adjusted to the same level of sperm concentration.

Conclusions1. Extra-cellular respiration was exhibited by seminal plasma of the boar. Oxygen consumption of seminal plasma ranged from 5 to 22% of that of the whole semen. The R.Q. was unity. After the plasma had been held for 5 minutes at 100°C respiration at reduced intensity was observed. Respiration was not exhibited by that fraction of the seminal plasma which passed through a porcelain filter. 2. The metabolic rate of the ejaculate of a cryptorchid boar was of the same order as that of seminal plasma. 3. No errors in measurement of oxygen consumption were detected which could be attributed to the presence of bacteria.