Urinary surface tension measurements were made in several normal subjects at hourly intervals. In order to eliminate the influence exerted by exercise and food, the subjects were kept in bed for a few hours preceding measurements. During this period, and the entire period of the experiment, the subjects were permitted to leave their beds each hour to void. Throughout the experiment, they were given the same kind and amount of food each hour. This eliminated as variable the influence of food and activity. Figures 218, 219 and 220 and Table XXVI show samples of the curves of surface tension in such cases. A 24-hour diphasic curve can be noted.

Surface tension in mice under similar conditions, however, shows differences. A group of 20 mice kept in cages were used. By slight squeezing of the lower abdomen, a few drops of urine were obtained in a little cup and used for surface tension measurement. Changes seen in Figure 221 show that with the passage of time, there is a dampening effect on the curve. This has made us doubt that the intervention of stress in these cases can be responsible for the changes. In order to eliminate stress as a factor, a second group of experiments was done in which urinary samples were obtained each hour from a different animal. Thus, each animal provided a sample of urine only once and was not under stress. Under these conditions, the dampening effect was not present. A curve showing only two phases in 24 hours was obtained. The ST curves for humans and mice are opposite. During the period when high values occur in humans, low values occur in mice, and vice versa. Because such opposite variations between humans and mice were found for many other analytical data and were considered related to the nocturnal activity of mice, a third group of experiments was performed in which the mice were kept in darkness during the day and under light during the night in an attempt to change the rhythm of their activity. After three weeks, there were no marked changes in analytical data obtained in these mice. It is possible, however, that more time is required to induce changes in surface tension by altering the rhythm of mouse activity. (Fig. 222)

24 hours hourly urinary surface tension value of a 30 year old normal male

Fig. 218. 24-hours hourly urinary surface tension value of a 30-year old normal male, kept resting and with a constant hourly food intake, showing a maximum in the afternoon and a minimum around 5 a.m.

Curve of the urinary surface tension in a 26 year old male

Fig. 219. Curve of the urinary surface tension in a 26-year old male on standardized hourly food and fluid intake showing a maximum toward the early morning hours and a minimum toward the evening.

urve of the urinary surface tension in a 27 year old female

Fig. 220. Curve of the urinary surface tension in a 27-year old female on standard hourly feeding, with a maximum in the afternoon and a minimum in the morning.

Average value of surface tension in the urine of 20 mice

Fig. 221. Average value of surface tension in the urine of 20 mice, obtained every hour, showing variations with a dampening character.

Table XXVI. Surface Tension In Normal Healthy 32 Year Old Man And 27 Year Old Female On Standard Hourly Feeding

Hour

Male S.T. in Dynes/cm.

Female S.T. in Dynes/cm.

7 a.m.

65

66

8 a.m.

64

67

9 a.m.

65

67

10 a.m.

67

69

11 a.m.

69

70

12 Noon

70

70

1 p.m.

71

72

2 p.m.

71

73

3 p.m.

71

73

4 p.m.

72

72

5 p.m.

73

73

6 p.m.

73

72

7 p.m.

72

71

8 p.m.

70

71

9 p.m.

69

70

10 p.m.

68

70

11 p.m.

67

67

12 Midnight

67

67

1 a.m.

66

67

2 a.m.

66

65

3 a.m.

65

65

4 a.m.

65

66

5 a.m.

63

66

6 a.m.

64

65

Surface Tension In Normal Humans And Animals

From the first analyses of urinary surface tension in groups of individuals it could be seen that certain changes common for all were taking place. There were days when all subjects had higher relative values and other days when lower values prevailed. Since there was no common dietetic or habit factor for all the subjects studied, we searched for environmental changes that might be the immediate cause of these variations. In collaboration with P. Teitelbaum we made the following experiment, using 80 rats divided into four groups. One group consisted of females of the Wistar strain and a second consisted of males of the same strain. The remaining two groups were composed of 20 females and 20 males of a black hooded strain. The animals were maintained in groups of five in separate cages on Purina and water ad lib. They were kept in a nonconditioned room. The experiment was conducted for one month, from May to June.

Average hourly values in the urinary surface tension of groups of 5 mice

Fig. 222. Average hourly values in the urinary surface tension of groups of 5 mice, the group being changed each hour.

Urine was collected in a small vessel by keeping the animal firm and pinching the lower abdominal skin. Surface tension was measured a few minutes later. In each group, animals which did not give urine under this procedure for several consecutive days were replaced by others.

Samples of urine were obtained 6 days a week, between 9 and 10:30 in the morning. From the data obtained, an average value was calculated for each group, and the respective values were plotted in curves having the days as abscissae. The values for the female group were higher than for males. No differences were seen between the two strains. And all four curves showed the same variations at the same times. Thus it appeared clear that the variations were related to some external factor acting upon all the animals. We compared the ST curves with others traced for different environmental values present at the time of observation. Such valuesóbarometric pressure, electrostatic value and temperatureówere obtained from the Weather Bureau and the curves for the area at the hour of the experiment traced. Of them all, only the curve for temperature change was significant. The ST was seen to rise each time that the temperature fell and fall when the temperature rose. (Fig. 223)

This correlation was further studied by using induced rather than natural temperature changes in the following experiment which was made in collaboration with E. F. Taskier.

Adult female CFi strain mice were divided into three groups of 20 mice each. They had ad lib access to food and water. One group was placed in an incubator in which the temperature was maintained at 37°C. A second group was kept in a refrigerator at 8°C. The third group served for control and was maintained at ordinary laboratory temperature which ranged between 20-25°C.

Because of the diurnal pattern of surface tension variations, urine specimens were collected at the same hour every day. During a period of 22 days, daily urine specimens were obtained between 9 and 11 A.M. This was easily accomplished by firmly gripping a mouse in one hand by the scruff of the neck and tail. With the finger of the other hand, the lower abdomen was gently massaged, causing the animal to void 2-5 drops of urine into a small glass cup.

Comparison between weather data and the average value of the surface tension in 40 male rats and 40 female rats

Fig. 223. Comparison between weather data and the average value of the surface tension in 40 male rats and 40 female rats. It shows a relative parallelism with the curve of the barometric pressure and a more consistent relationship with the inverse curve of the temperature.

The surface tension of each specimen was determined within a few minutes after it was obtained.

The values obtained from day to day were charted for each individual mouse; the average for each group maintained under different temperature conditions also was determined.

Average value of surface tension of the urine in control mice over a period of 3 weeks

Fig. 224. Average value of surface tension of the urine in control mice over a period of 3 weeks.

The average surface tension readings in the control groups are shown in Figure 224. It can be seen that these values fluctuated in an irregular fashion between 58 and 63 dynes/cm. The surface tension values of the group maintained at 37°C show a steady sustained rise from 61 to 65 dynes/cm. (Fig. 225) The mice kept at 8°C showed an initial slight fall in surface tension, with a gradual return to the original levels. (225)

After several days in the incubator, the mice began to lose weight, their fur became sparse, and snout areas were constantly wet. The urinary output was scanty as compared with the two other groups. Death began to occur in the mice kept a high temperature on the 12th day. The animals in the refrigerator developed thick luxuriant coats and huddled closely together at most times. None died from exposure to this temperature.

The fact that the animals maintained at 37°C showed a steady rise in urinary surface tension was especially significant. As expected, the urine of these animals was scanty and more concentrated than for the other groups. With this diminution in volume, it would be expected that the concentration of surface active substances would rise and the surface tension would be lowered. The fact that the exact opposite occurred indicates that the observed change has to be considered as an effect of the high temperature.

This appears especially interesting for the relationship between temperature and the two ST patterns. While higher temperature induces one pattern, cold induces the other. It must be noted that the organism cannot defend itself against the pattern induced by higher temperature and the animal dies after a certain time, but for the pattern induced by cold, defense is possible. The body seems to be able to overcome the change. The surface tension returns to normal and the animal becomes adapted to the temperature. Not one of the animals kept in the refrigerator died, while all in the incubator were dead after a month. Adrenalectomy induces an immediate increase in the surface tension of the urine. (Fig. 226)

The average values of the urinary surface tension of 20 female mice kept in the incubator at 37

Fig. 225. The average values of the urinary surface tension of 20 female mice kept in the incubator at 37°C. and of 20 female mice kept in refrigerator at 8°C. The values are progressively increasing for the animals kept in the incubator until the animal died. For the animals kept in refrigerator, after an initial descent, the values ascend toward normal.

The surface tension of the urine increases to high values after adrenalectomy

Fig. 226. The surface tension of the urine increases to high values after adrenalectomy.

Curve of the surface tension changes in urine specimens of a 36 yr. old pregnant woman

Fig. 227. Curve of the surface tension changes in urine specimens of a 36-yr. old pregnant woman shows a manifest change toward low values, starting with the 4th month, and becoming especially low in the last three months.

The average value of the surface tension in pregnant women shows a manifest change toward low values

Fig. 228. The average value of the surface tension in pregnant women shows a manifest change toward low values.

Colloids In Urine And Surface Tension

An interesting relationship between urinary surface tension and the presence of "colloids" in the urine was noted by Butt and his associates. (240) Using the pendant drop method for the ST, direct examination in dark field for the presence of colloids in the urine, electrophoresis for determination of electrical charges, and the study of evaporated urine smears, they showed that urines with a high content of colloids, have a low ST; those with a low colloid content, a high ST. They have further correlated a low amount of colloids with a tendency of urine to precipitate and form stones. (242) They examined the colloid particles in the urine of different groups of individuals and found them high in Negroes, and especially high in pregnant women, which is in accord with the low surface tension of the urine which we found in these cases (Figs. 227 and 228) and the low tendency of both groups to form urinary stones.

We were interested in the relationship between variations in the urinary content of colloids and systemic patterns corresponding to high and low ST. R. Ravich in our laboratory has confirmed the correlation between presence of colloids and ST by using our urotensiometer. (219)