A considerable amount of experimental evidence has accumulated regarding the relationship of the average basal values of different individuals.1 The comparison of the results obtained with different subjects has been much discussed, together with the varying effects upon them of the factors influencing the basal metabolism, such variations depending upon the different conditions of nutriment and environment. Here, however, we are particularly interested only in those factors which influence the basal metabolism of a single individual. The question arises: To what extent is it possible to determine the basal metabolism of a subject and assume that this value is constant and may be logically used as a general base-line for food experiments subsequently carried out?

When several basal experiments have been made with a subject, and a number of closely agreeing results have been obtained for that particular day, many investigators use this average basal value for comparison with results obtained on subsequent days without further comment. The short-period method admits of the duplication of experimental periods for comparison in securing an average basal value, but it is by no means certain that the general use of such a value is the wisest or the most satisfactory procedure.

It is obvious that the metabolism will be somewhat affected by a material alteration in the body-weight, such as may take place in the course of a year or, with a growing individual, in a very much shorter space of time. A base-line determined under materially different weight conditions may not therefore be used for general comparison.

Furthermore, seasonal variations may be possible. For example, we may ask whether a base-line determined in the winter may be logically used for comparison in the summer. One of the most striking illustrations of seasonal variation was given in some observations made at the Massachusetts General Hospital upon Palmer.2 With essentially the same body-weight, the subject showed in summer a total heat production of 1,797 calories, 19.2 calories per kilogram of body-weight, and 707 calories per square meter of body-surface; in winter he had a total heat production of 2,004 calories, 21.4 calories per kilogram of body-weight, and 789 calories per square meter of body-surface.

The question of possible seasonal variation has also been considered in connection with the results of our short-period experiments. To this end the values obtained for the consumption of oxygen per minute in the individual months have been averaged in table 46 for each subject who was studied during a period of at least 7 1/2 months. The longest period of time during which experiments were made was that for L. E. E. of 6 1/4 years. With none of the subjects were values obtained for every month in the year. The primary object in giving these average values is to note if there is a tendency for the metabolism to be distinctly higher at one season than another.

1Benedict, Emmes, Roth, and Smith, Journ. Biol. Chem., 1914, 18, p. 139; Benedict, ibid., 1915, 20, p. 263. 2Palmer, Means, and Gamble, Journ. Biol. Chem., 1914, 19, pp. 242 and 243.

Table 46. - Average Oxygen Consumption In Different Months Of The Year In Respiration Experiments Without Food.1

(Values per minute).

1This table includes all subjects on whom experiments were made during a period of at least 7 1/2 months, the longest period being 6 1/4 years with subject L. E. E. 2See explanation of this high value on page 103.

Examining the data for differences from month to month, we find that with H. H. A. the minimum of 200 c.c. occurs in November and that the maximum of 220 c.c. is found in March, with a difference of 10 per cent. In this particular case, therefore, the basal value determined in November can not properly be used for studying small increments measured in March. It does not follow, however, that we should invariably expect with H. H. A. a low metabolism in November with a higher metabolism in March.

With the subject K. H. A. the variations are extremely small; the minimum value (230 c.c.) was found in February and the maximum (249 c.c.) in March. With F. G. B. a minimum of 243 c.c. was found in May and a maximum of 268 c.c. in April; with J. J. C. a minimum of 218 c.c. in May and a maximum of 235 c.c. in January and March; with T. M. C. a minimum of 176 c.c. in July and a maximum of 191 c.c. in November. The values for A. G. E. are practically constant for the 5 months during which he was measured. With L. E. E. a minimum of 237 c.c. was obtained in July and a maximum of 263 c.c. in November; with H. L. H. a minimum of 233 c.c. in June and a maximum of 264 c.c. in September; with P. F. J. a minimum of 219 c.c. in July and a maximum of 251 c.c. in April; with Dr. M. a minimum of 232 c.c. in June and a maximum of 290 c.c. in April; with J. K. M. a minimum of 220 c.c. in July and a maximum of 236 c.c. in September; with M. A. M. a minimum of 237 c.c. in December and a maximum of 251 c.c. in March; with H. F. T. a minimum of 184 c.c. in August and a maximum of 205 c.c. in June; while with J. B. T. a minimum was found of 244 c.c. in October and a maximum of 281 c.c. in December. It is thus clear that the metabolism of these subjects, as indicated by oxygen measurements alone, does not show regular seasonal variations, but only noticeable differences in averages from month to month.

Although in table 46 we have recorded only the oxygen measurements, yet it is evident that with these normal individuals the respiratory quotient in the post-absorptive condition remains reasonably uniform at 0.85, so that for purposes of comparison we may assume that the oxygen consumption corresponds to the heat production. While, therefore, the data show somewhat large differences in the metabolism for the different months with different individuals, there is no uniformity other than the possible tendency for the high values to fall in the month of March, this occurring with four subjects, and for the minimum metabolism to fall in July, as also found with four subjects; but the results are not sufficiently uniform to draw definite conclusions as to the maximum and minimum metabolism occurring in these two months.