10 were kept in a temperature' varying from 6°-8°c below
their optimum the first month and 4°-7°c below the second.
The results are given in table II, which show that the tadpoles
enjoying their optimum increase more rapidly in both weight
and length. 2

It appears then that optimum temperature, maximum met-
abolism and most rapid growth are causally related; another

TABLE II.

Showing the rate of growth of ten tadpoles in their optimum temperature, and of ten others in 4°c.-8°c. below the optimum.

Gain. Length. Gain. Weight. Gain. Length. Gain.

Difference of Increase.

Wt. Length

inference is, that the optimum is chosen because that particular
temperature is a factor in the organism's well-being, that it
affords just that temperature stimulus necessary to set agoing
the physico-chemical activities in harmony with that pitch or
rhythm which natural selection has determined for that species.
The same interpretation, in the absence of conflicting evidence,
may be extended to all thermotactic organisms, i. e., a positive
thermotactic response is an effort of the organism, guided by
the "differences in the intensity of heat to which the two poles

1 Two glass jars of same shape and size were used. They contained equal quantities of tap water into which was put same kind and as near as possible equal amounts of grasses and foods. The jar, in which it was desired to keep a known and constant temperature, was placed in a copper kettle containing on an average nine liters of water. The bottom of the glass jar barely touched the surface of the water. In this way the temperature of the water in the jar was maintained between 20°c-23°c. The temperature of the second jar varied with that of the room, which during the months through which the experiment extended fluctuated between 129-18°c. The experiment was extended through the months of February and March, but serious and frequent mishaps set in that rendered the results worthless. Although the experiment ran smoothly during the months reported, the force of the results is weakened by the short period of the experiment.

2 Drs. Davenport and Castle report tadpoles as growing more rapidly under constant temperature of 24°-25°, then those subjected to 150c. The results of my experiment had been described some time before their work came into my hands.

JOURNAL-2

Time.

Air aspirated.

TABLE I.

Showing the amount of CO produced per hour per kilogram of Tadpole at different temperatures.

Experi- 'No. of ment. tadpoles.

60.64

་་

88 G

. 180 G

. 1980 G.0756 G 859

་་

220°

6,1 ΙΟ 5
1 The tadpoles were in a high state of feeding, and undergoing rapid metamorphosing. Chapman and Bru-
baker have shown that in the case of two pigeons, one, fat and well fed, produced per hour twice as much CO2
as the second, poorly fed and lean in flesh. Further, Richet-Archiv. de Phys. Normale et Pathologique, 5th
ser., Vol. II, pp. 17-30, 1890- has showu that in the same species the quantity of CO, exhaled is inversely pro-
portioned to the body weight and directly proportioned to the body surface. In the above calculations the
weight of ten tadpoles is treated in the calculations as though it were the weight of a single animal. It is
evident that when the sum of the body weights of any two animals equals that of a third animal, their body
surface is much larger and according to Richet's law exhale more CO2 than a single animal of equal weight.
To illustrate: Take the weight of the ten tadpoles of experiment and regard it as the weight of one animal,
the body surface would be 226.24 sq. cm., but regarded as the weight of ten animals of the same species the body
surface equals 470.4 sq. cm., or twice the area of a single animal of that weight. It is evident that a plus cor-
rection for body weight might properly be made and thus lower the amount of CO2 exhaled per kilo. of animal.

1

portion," and that found in the latter the "gravimetric portion." The sum of the two being the whole amount exhaled. A detailed statement of the experiment and results are given in Table I. This Table shows that a maximum amount of CO2 is produced at the optimum, 20°c, and that the amounts decrease for temperatures above and below the optimum and further that the fall is much more rapid toward the lower temperatures than toward the higher ones. [See Curve in Chart II.] If then we regard the production of CO2 as a fair index of the amount of normal metabolism in an organism we are justified in the conclusion that for this species of embryos, maximum metabolism is coincident and very probably a function of optimum temperature. Page's experiments on the dog show that a minimum amount of CO, is produced in a temperature of 25°c and that the amount increases above and below 25°c, which is probably about the optimum for this mammal. [See Curve in Chart II.] Thus the warm3 blooded animal presents reverse conditions. 4 The fact emphasized here, however, is tubes and a large Waulff flask. The first and seventh tube contained concentrated sulphuric acid and pumice stone, the first caught any organic matter issuing from the jar containing the tadpoles, the seventh caught organic and moist particles coming from the Waulff flask at times of a negative pressure, the remaining five tubes contained potassium hydrate slightly moistened. The difference in the weight of these tubes thoroughly dried and corked, before and after the aspiration is the weight (with one correction) of the CO2 that escaped from the

water.

The estimation of the amount of CO, that remained behind in the water was made by the quantitative method devised by Pettenkorfer, (For description see Fresenius, Quant. Anal., Amer. Ed., p. 834.)

'The water to be tested was siphoned from the jar into a 100 cc burette and from thence into a bottle corked with ground glass. The CO2 of the air in the room and of the water used was deducted from the sum of the "volumetric" and "gravimetric" portions. The air aspirated was corrected for temperature and pressure. The CO, in the room was determined by both the Lunge and Regnault methods. The CO2 of the tap water was determined by the Pettenkorfer method. 2 Page: External temperature affecting the amount of CO2, Jour. of Phys., Vol. II, p. 228, 1879-80.

3 Body temperature of warm blooded animals is kept constant by all parts of the body being constantly oxidized, so that when the external temperature is low much burning is needed to maintain the requisite temperature, and consequently much carbon produced; also if the external temperature is above that of the body it hastens oxidation. That the relative amounts of CO2 produced at any temperature below the optimum for cold blooded animals should bear a direct proportion to that temperature is evident, but why the amount should decrease above the optimum is not so clear. It is suggested that probably the higher temperatures destroy or disorganize the normal physico-chemic life processes, since the heat rigor of tadpoles is reached at 348-35°c.

4 Edward Smith shows that the quantity of CO2 given off in man is inverse as the change of the temperature; the vital changes lessening with increase of temperature. Food, p. II.

that there is a comparatively fixed rate of metabolism in opti-
mum temperature for both species.

The next question of importance is, what effect has maximum

CHART II.

Curves showing the relation of the production of CO2 at different tem-
peratures for dog and tadpole.

DOG

TADPOLES

1° 2° 3° 4° 5° 6° 7° 8° 9° 10° 11° 12°13°14° 15°16° 17°18°19°20°21°22°23°24° 25° 26°27°28°29°30°31°32°33°34°35°

metabolism on the tadpole, as a whole? To secure experi-
mental evidence on this point a group of ten tadpoles was sub-
jected to their optimum for two months. A second group of

10 were kept in a temperature' varying from 6°-8°c below
their optimum the first month and 4°-7°c below the second.
The results are given in table II, which show that the tadpoles
enjoying their optimum increase more rapidly in both weight
and length. 2

It appears then that optimum temperature, maximum met-
abolism and most rapid growth are causally related; another

TABLE II.

Showing the rate of growth of ten tadpoles in their optimum tempera-
ture, and of ten others in 4°c.-8°c. below the optimum.

In Optimum.

Below Optimum.

Difference of Increase.

Gain. Length. Gain. Weight. Gain. Length. Gain.

Wt. Length

inference is, that the optimum is chosen because that particular
temperature is a factor in the organism's well-being, that it
affords just that temperature stimulus necessary to set agoing
the physico-chemical activities in harmony with that pitch or
rhythm which natural selection has determined for that species.
The same interpretation, in the absence of conflicting evidence,
may be extended to all thermotactic organisms, i. e., a positive
thermotactic response is an effort of the organism, guided by
the "differences in the intensity of heat to which the two poles

1 Two glass jars of same shape and size were used. They contained equal quantities of tap water into which was put same kind and as near as possible equal amounts of grasses and foods. The jar, in which it was desired to keep a known and constant temperature, was placed in a copper kettle containing on an average nine liters of water. The bottom of the glass jar barely touched the surface of the water. In this way the temperature of the water in the jar was maintained between 20°c -23°c. The temperature of the second jar varied with that of the room, which during the months through which the experiment extended fluctuated between 12-18°c. The experiment was extended through the months of February and March, but serious and frequent mishaps set in that rendered the results worthless. Although the experiment ran smoothly during the months reported, the force of the results is weakened by the short period of the experiment.

2 Drs. Davenport and Castle report tadpoles as growing more rapidly under constant temperature of 24-25°, then those subjected to 150c. The results of my experiment had been described some time before their work came into my hands.

JOURNAL-2