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Heart Rate of the Domestic Fowl
Heart Rate of the Domestic Fowl E. H.
MCNALLY
U. S. Department of Agriculture, Beltsville Research Center, Beltsville, Maryland (Received for publication September 30, 1940)
T
HE heart rate of the adult domestic fowl has not been measured except in a few isolated physiological experiments where comparisons have been made during growth (Bogue, 1933) or with other species (Buchanan, 1910). These studies have not been sufficiently complete to enable one to given even approximate figures for the common breeds or for the sexes of the same breed. This has been partially due to the fact that the rate is difficult to determine with the stethoscope because of its rapidity, and because special equipment must be employed and this has not been generally available. During recent years the electrocardiotachometer, developed mainly for the study of the rate of the human heart, has been modified by several investigators making it possible to measure the rapid heart rate of small animals. A summary of previous recorded heart rates of the domestic fowl is given in Table 1.
thetized birds, using a Ludwig manometer. The heart rate was recorded by Buchanan (1910) for a large number of birds and small mammals by using the electrical impulse of the heart with a capillary electrometer. EXPERIMENTAL
An electrocardiotachometer, set up and used in conjunction with experiments on the effect of ionized air on poultry, was subsequently used in the study of heart rates of normal fowl reported in this paper. The apparatus was similar to that described by Horton (1938), modified to allow for the balancing of the tubes in the relay circuit. In some experiments the heart rate was read directly from the meter and in others a small aluminum lever was attached directly to the relay to give kymograph recordings. The electrical impulse of the heart was obtained from the birds by using 3- to 4-inch copper needle electrodes under the skin, one beside the crop and the other
TABLE 1.—Previously recorded heart rates of the domestic fowl Type of fowl
Adult cock Hen when at rest Adult hen New Hampshire h e n s . . . . Hen
Heart rate Beats per minute App. 320 Ave. 339 (10)* Ave. 289±38.9 (4)* 300 App. 330 Ave. 286 (19)* Ave. 195 (29)* Ave. 200+18.7(23)*
Authority Bogue (1933) Stiibel (1910) Boas and Landauer (1933) Bogue (1932) Buchanan (1910) Stiibel (1910) Winchester (1940)
* Number of birds studied.
Bogue (1932) determined the heart rate by using the string electrocardiograph while Stiibel (1910) made kymograph records from the blood pressure changes of anes-
along the leg and abdominal wall. The use of needle electrodes was not considered altogether satisfactory, but the use of metal gauze or other electrodes in contact with the
[266]
HEART RATE OF THE DOMESTIC FOWL
240 I P.M.
4 RM.
267
8 A.M. II A.M. 12 4 A.M. HOUR OF DAY FIG. 1. Heart rate in beats per minute of a Single Comb White Leghorn hen from 1:30 p.m. until 11:00 a.m. the next day. Dark period shown with bar. 8 P.M.
skin did not give an electrical impulse strong enough to trip the amplifier circuit. Even with needle electrodes the relay circuit would sometimes trip itself automatically due to the small electrical impulse from the hearts of certain birds and a stethoscope was accordingly used to check the synchronization, of the relay beat with that of the heart. When birds were observed for several hours or longer they were placed in batteries and the electrode wires were suspended from above by rubber bands which allowed freedom of movement. The typical course of heart rate of a White Leghorn hen from 2:00 p.m. until 10:00 a.m. the following day is shown in Figure 1. Readings were taken from the meter at 10-minute intervals. The hens were in batteries with feed and water available so that the normal activities were carried on. A fluctuation of heart rate from less than 280 to more than 340 beats per minute was observed. The gradual decrease in the heart rate as the hen became quiet for the night and while it
was asleep is similar to that found in men and women by Boas (1932) who reported that a minimum heart rate occurred after 5 or 6 hours' sleep. This minimum heart rate, found during the early morning hours (1 to 3 a.m.) was as low as 160 beats per minute in Rhode Island Red males. The diurnal periodicity of heart rate is similar to the diurnal rhythm of body temperature changes as reported by Fronda (1925). Eating and movements in the cage were associated with fluctuations in heart rate. Psychic influences were also reflected in these fluctuations. The distant crowing of a cock would cause an increase in the heart rate, especially during the early morning hours. In view of the rapidity of short time fluctuations shown in Figure 1 it is difficult to see how one would obtain a so-called basal heart rate. Bogue (1933) found that even strict isolation of a chick caused increased activity with an increase in the heart rate. In order to determine if breed or sex
268
E. H.
MCNALLY
TABLE 2.—Average minimum resting heart rates of S. C. White Leghorn hens (beats per minute) headings on alternate day Bird no. 1677 1783 1770 1798 1687 1785
Ave.
1
3
5
7
9
11
336 300 324 348 372 372
300 336 324 360 396 384
300 336 312 360 348 372
300 336 336 312 336 348
288 300 324 312 360 360
288 318 312 348 300 360
had an influence upon heart rate, six adult hens and six adult cocks of both Rhode Island Red and White Leghorn breeds were studied. Kymograph records of four to five minutes in duration were made of the heart rate on alternate days three times a week for two weeks, giving six records for each bird. The birds were removed from the batteries and tied upon an operating table in the laboratory during the time the record was taken. A dark cloth was placed over the bird to shut out the light and to keep it quiet. The birds rested reasonably quietly during this time although such movement or excitement as occurred was Beflected by an increase of the heart rate. The room was kept as quiet as possible before and during the recording. At the termination of the last recording the Rhode Island Reds were killed and the heart weights determined. The resting heart rate for the four- or five-minute period recorded by the kymograph was taken as the rate maintained during the 10-second period of lowest rate found among 14 or IS of the recorded 10-
302 321 322 340 352 366
second periods. This procedure apparently eliminated any period of movement or excitement. The daily resting heart rates of the Leghorn hens on alternate days and the average resting heart rate for each hen over the entire period are given in Table 2. A higher rate is noticeable during the first or second recording with a tendency toward lower rates as the novelty of the situation became less. Although the daily variation is quite large each bird seems to show a characteristic rate. The heart rate in hen number 1687, 396 beats per minute, is the highest that was observed in resting birds. Under conditions of excitement, however, rates of over 400 heats per minute were observed in adult birds on several occasions. The average heart rates of the hens of both breeds (White Leghorn and Rhode Island Red) for the six readings have been tabulated and are given with live weight of each bird in Table 3. A notable difference is observed in the heart rates of the two breeds, the Leghorns having a pronouncedly higher rate
TABLE 3.—Average minimum resting heart rates of Rhode Island Red and S. C. White Leghorn hens {beats per minute)
R. I. R. number
Ave. heart rate
Body wt. gms.
W. L. number
Ave. heart rate
Body wt. gms.
934 939 938
247 262 284 288 296 296
2140 2160 2420 2070 2100 2180
1677 1783 1770 1798 1687 1785
302 321 322 340 352 366
1510 1710 2060 1460 1480 1440
1566 8732 8731
269
HEART RATE OF THE DOMESTIC FOWL
TABLE 4.—Average minimum resting heart rates of Rhode Island Red and S. C. White Leghorn cocks {beats per minute) R. I. R. number
Ave. heart rate
Body wt. gms.
W. L. number
Ave. heart rate
Body wt. gms.
1608 2845 1598 1601 2772 2700
226 236 242 246 254 258
2450 3120 2640 2550 2760 2940
124 6 34 461 152 475
247 256 258 280 280 318
2160 2280 1940 2060 1880 2250
Ave.
243.7
2743
Ave.
273.1
2095
than the Rhode Island Reds. The heart rates of the males have been tabulated similarly to that of the females and are given with body weight of each bird in Table 4. The breed difference is not so evident in the males as in the females. When the females and males of the same breed are compared, an increased heart rate for the females, of about the same magnitude as the difference between these two breeds, is observed. The lowest heart rate observed in this series of recordings was that of a Rhode Island Red male with a rate of 192 beats per minute. In long-time observations heart rates as low as 160 beats per minute have been recorded on Rhode Island Red males in the early morning hours when they were asleep or at rest. Partial correlations between heart rate and body weight have been computed by the method of co-variants, and the correlations are given in Table 5. TABLE 5.—Partial correlations by co-variants of heart rate and body weight
Sources of variation
Corr. coeff.
Highly significant values of r*
Total Within the b r e e d s . . . . Between the breeds. .. Within the sexes Between the s e x e s . . . .
.77 .64 .999 .63 .999
.505 .515 1.000 .515 1.000
* From Table 16 in Wallace and Snedecor.
These correlations are all highly significant. While both breed and sex are found to be associated with differences in heart rate, these relations are possibly to be conceived . •
y42i :6-.06£ X
^•
' ..
>s
. *£00
2P00 2200 2.400 2SOO LIVE WEIGHT '(GRAMS)
2300
3,000 1200
FIG. 2. Relationship of heart rates per minute and live weight for Rhode Island Red and Single Comb White Leghorn hens and cocks.
as secondary to a more general relation between body weight and heart rate. The small White Leghorn females have the fastest rate and the large Rhode Island Red males have the slowest rate. The Rhode Island Red females and the White Leghorn males of somewhat similar body weight have about the same heart rate. The relation between body weight and heart rate has been plotted in Figure 2. The line of regression has been calculated by the method of least squares and has been found
270
E. H. MCNALLY
to be 422.6 - 0.06SX DISCUSSION The increase in heart rate with a decrease in body size has already been pointed out for different species of birds and mammals by Buchanan (1910) and Clark (1927). When the heart rate of the fowl is compared with that of other species it is found to be much faster than would be expected for a bird of its body weight. The percentTABLE 6.-
-Percentage heart weight and heart rate of certain mammals and birds*
Type of animal
Percentage heart weight of body weight*
Heart beats per minute*
0.59 0.75 0.45
70 120 160
1.36 1.5 0.63 0.35
800 185 240 261
Mammals: Medium-sized dog. . . Birds: Sparrow Pigeon Duck (tame) Fowl (R.I.R.)
* Compiled and modified from Buchanan's (1910) data, except R.I.R. fowl.
age of heart weight to body weight, and rate of metabolism in relation to body weight are complicating factors that may under certain conditions give smaller birds a slower or more rapid heart rate. The rapid heart rate of the fowl would appear to be partially due to the small percentage heart weight. Comparative figures for the percentage heart weight and heart rate of different species of animals are given in Table 6. In these data the rapid heart rate and the remarkably small percentage heart weight of the fowl are well displayed. The small weight of the heart of the domestic fowl seems to be a characteristic of domestic animals in general. The Rhode Island Reds used in our experiment had remarkably
small hearts. Buchanan (1910) states: "The relatively small heart of animals kept for food, such as the hen, the tame duck, the pig, the ox, and the cow is on the other hand a consequence of the artificial fattening up of these animals, thus increasing their body weight, while their hearts, having little to do, do not keep pace, it being possible to supply the oxygen demanded by increasing the frequency of beat." Clark (1927) also pointed out that active animals capable of severe and continued exertion have a higher percentage heart weight than inactive animals. SUMMARY
Observations were made on the heart rates of 12 Rhode Island Reds and 12 Single Comb White Leghorns, 6 males and 6 females of each breed, using the electrocardiotachometer of Horton. The average heart rate for all the birds of both breeds and sexes was found to be 282 beats per minute during the day, ranging from a low of 192 in a Rhode Island Red male to a high of 396 in a White Leghorn female. In longtime observations a minimum heart rate was found during the early morning (1 to 3 a.m.), as low as 160 beats per minute being recorded in Rhode Island Red males. A correlation holds between body weight and heart rate which appears to be more fundamental than either breed or sex differences in the two breeds studied, heavier birds showing a slower heart rate. The heart weight-body weight ratio calculated for the Rhode Island Red birds was observed to be lower than that reported for any other wild or domestic bird. REFERENCES
Boas, E. P., and E. F. Goldsmidt, 1932. The heart rate. C. C Thomas, Pub., Baltimore. Boas, E. P., and W. Landauer, 1933. The effect of elevated metabolism on the heart of frizzle fowl. Amer. Jour. Med. Sci. NS. 185:654.
HEART RATE OF THE DOMESTIC FOWL Bogue, J. Y., 1932. The heart rate of the developing chick. J. Exp. Biol. 9:351. , 1933. The electrocardiogram of the developing chick. J. Exp. Biol. 10:286. Buchanan, F., 1910. Significance of the pulse rate in vertebrate animals. Ann. Rpt. Smithsonian Inst., p. 484. Clark, A. J., 1927. Comparative physiology of the heart. Cambridge Univ. Press. Fronda, F. M., 1925. Some observations on the body temperature of poultry. Cornell Vet. IS :8-20.
271
Horton, J. W., 1938. An electronic cardiotachometer. Electronics, Aug. 1938. Stiibel, H. S., 1910. Beitrage zur Kenntnis der Physiologie des Blutkreislaufes bei verschiedenen Vogelarten. Pfluger's Arch, f .d. ges Physiol. 13S :249. Wallace, H. A., and George W. Snedecor, 1931. Correlation and Machine Calculation Rev. Iowa State College of Agriculture. Winchester, C. F., 1940. Seasonal, metabolic, and endocrine rhythms in the domestic fowl. Missouri Agri. Sta. Res. Bull. 315.
MCNALLY
U. S. Department of Agriculture, Beltsville Research Center, Beltsville, Maryland (Received for publication September 30, 1940)
T
HE heart rate of the adult domestic fowl has not been measured except in a few isolated physiological experiments where comparisons have been made during growth (Bogue, 1933) or with other species (Buchanan, 1910). These studies have not been sufficiently complete to enable one to given even approximate figures for the common breeds or for the sexes of the same breed. This has been partially due to the fact that the rate is difficult to determine with the stethoscope because of its rapidity, and because special equipment must be employed and this has not been generally available. During recent years the electrocardiotachometer, developed mainly for the study of the rate of the human heart, has been modified by several investigators making it possible to measure the rapid heart rate of small animals. A summary of previous recorded heart rates of the domestic fowl is given in Table 1.
thetized birds, using a Ludwig manometer. The heart rate was recorded by Buchanan (1910) for a large number of birds and small mammals by using the electrical impulse of the heart with a capillary electrometer. EXPERIMENTAL
An electrocardiotachometer, set up and used in conjunction with experiments on the effect of ionized air on poultry, was subsequently used in the study of heart rates of normal fowl reported in this paper. The apparatus was similar to that described by Horton (1938), modified to allow for the balancing of the tubes in the relay circuit. In some experiments the heart rate was read directly from the meter and in others a small aluminum lever was attached directly to the relay to give kymograph recordings. The electrical impulse of the heart was obtained from the birds by using 3- to 4-inch copper needle electrodes under the skin, one beside the crop and the other
TABLE 1.—Previously recorded heart rates of the domestic fowl Type of fowl
Adult cock Hen when at rest Adult hen New Hampshire h e n s . . . . Hen
Heart rate Beats per minute App. 320 Ave. 339 (10)* Ave. 289±38.9 (4)* 300 App. 330 Ave. 286 (19)* Ave. 195 (29)* Ave. 200+18.7(23)*
Authority Bogue (1933) Stiibel (1910) Boas and Landauer (1933) Bogue (1932) Buchanan (1910) Stiibel (1910) Winchester (1940)
* Number of birds studied.
Bogue (1932) determined the heart rate by using the string electrocardiograph while Stiibel (1910) made kymograph records from the blood pressure changes of anes-
along the leg and abdominal wall. The use of needle electrodes was not considered altogether satisfactory, but the use of metal gauze or other electrodes in contact with the
[266]
HEART RATE OF THE DOMESTIC FOWL
240 I P.M.
4 RM.
267
8 A.M. II A.M. 12 4 A.M. HOUR OF DAY FIG. 1. Heart rate in beats per minute of a Single Comb White Leghorn hen from 1:30 p.m. until 11:00 a.m. the next day. Dark period shown with bar. 8 P.M.
skin did not give an electrical impulse strong enough to trip the amplifier circuit. Even with needle electrodes the relay circuit would sometimes trip itself automatically due to the small electrical impulse from the hearts of certain birds and a stethoscope was accordingly used to check the synchronization, of the relay beat with that of the heart. When birds were observed for several hours or longer they were placed in batteries and the electrode wires were suspended from above by rubber bands which allowed freedom of movement. The typical course of heart rate of a White Leghorn hen from 2:00 p.m. until 10:00 a.m. the following day is shown in Figure 1. Readings were taken from the meter at 10-minute intervals. The hens were in batteries with feed and water available so that the normal activities were carried on. A fluctuation of heart rate from less than 280 to more than 340 beats per minute was observed. The gradual decrease in the heart rate as the hen became quiet for the night and while it
was asleep is similar to that found in men and women by Boas (1932) who reported that a minimum heart rate occurred after 5 or 6 hours' sleep. This minimum heart rate, found during the early morning hours (1 to 3 a.m.) was as low as 160 beats per minute in Rhode Island Red males. The diurnal periodicity of heart rate is similar to the diurnal rhythm of body temperature changes as reported by Fronda (1925). Eating and movements in the cage were associated with fluctuations in heart rate. Psychic influences were also reflected in these fluctuations. The distant crowing of a cock would cause an increase in the heart rate, especially during the early morning hours. In view of the rapidity of short time fluctuations shown in Figure 1 it is difficult to see how one would obtain a so-called basal heart rate. Bogue (1933) found that even strict isolation of a chick caused increased activity with an increase in the heart rate. In order to determine if breed or sex
268
E. H.
MCNALLY
TABLE 2.—Average minimum resting heart rates of S. C. White Leghorn hens (beats per minute) headings on alternate day Bird no. 1677 1783 1770 1798 1687 1785
Ave.
1
3
5
7
9
11
336 300 324 348 372 372
300 336 324 360 396 384
300 336 312 360 348 372
300 336 336 312 336 348
288 300 324 312 360 360
288 318 312 348 300 360
had an influence upon heart rate, six adult hens and six adult cocks of both Rhode Island Red and White Leghorn breeds were studied. Kymograph records of four to five minutes in duration were made of the heart rate on alternate days three times a week for two weeks, giving six records for each bird. The birds were removed from the batteries and tied upon an operating table in the laboratory during the time the record was taken. A dark cloth was placed over the bird to shut out the light and to keep it quiet. The birds rested reasonably quietly during this time although such movement or excitement as occurred was Beflected by an increase of the heart rate. The room was kept as quiet as possible before and during the recording. At the termination of the last recording the Rhode Island Reds were killed and the heart weights determined. The resting heart rate for the four- or five-minute period recorded by the kymograph was taken as the rate maintained during the 10-second period of lowest rate found among 14 or IS of the recorded 10-
302 321 322 340 352 366
second periods. This procedure apparently eliminated any period of movement or excitement. The daily resting heart rates of the Leghorn hens on alternate days and the average resting heart rate for each hen over the entire period are given in Table 2. A higher rate is noticeable during the first or second recording with a tendency toward lower rates as the novelty of the situation became less. Although the daily variation is quite large each bird seems to show a characteristic rate. The heart rate in hen number 1687, 396 beats per minute, is the highest that was observed in resting birds. Under conditions of excitement, however, rates of over 400 heats per minute were observed in adult birds on several occasions. The average heart rates of the hens of both breeds (White Leghorn and Rhode Island Red) for the six readings have been tabulated and are given with live weight of each bird in Table 3. A notable difference is observed in the heart rates of the two breeds, the Leghorns having a pronouncedly higher rate
TABLE 3.—Average minimum resting heart rates of Rhode Island Red and S. C. White Leghorn hens {beats per minute)
R. I. R. number
Ave. heart rate
Body wt. gms.
W. L. number
Ave. heart rate
Body wt. gms.
934 939 938
247 262 284 288 296 296
2140 2160 2420 2070 2100 2180
1677 1783 1770 1798 1687 1785
302 321 322 340 352 366
1510 1710 2060 1460 1480 1440
1566 8732 8731
269
HEART RATE OF THE DOMESTIC FOWL
TABLE 4.—Average minimum resting heart rates of Rhode Island Red and S. C. White Leghorn cocks {beats per minute) R. I. R. number
Ave. heart rate
Body wt. gms.
W. L. number
Ave. heart rate
Body wt. gms.
1608 2845 1598 1601 2772 2700
226 236 242 246 254 258
2450 3120 2640 2550 2760 2940
124 6 34 461 152 475
247 256 258 280 280 318
2160 2280 1940 2060 1880 2250
Ave.
243.7
2743
Ave.
273.1
2095
than the Rhode Island Reds. The heart rates of the males have been tabulated similarly to that of the females and are given with body weight of each bird in Table 4. The breed difference is not so evident in the males as in the females. When the females and males of the same breed are compared, an increased heart rate for the females, of about the same magnitude as the difference between these two breeds, is observed. The lowest heart rate observed in this series of recordings was that of a Rhode Island Red male with a rate of 192 beats per minute. In long-time observations heart rates as low as 160 beats per minute have been recorded on Rhode Island Red males in the early morning hours when they were asleep or at rest. Partial correlations between heart rate and body weight have been computed by the method of co-variants, and the correlations are given in Table 5. TABLE 5.—Partial correlations by co-variants of heart rate and body weight
Sources of variation
Corr. coeff.
Highly significant values of r*
Total Within the b r e e d s . . . . Between the breeds. .. Within the sexes Between the s e x e s . . . .
.77 .64 .999 .63 .999
.505 .515 1.000 .515 1.000
* From Table 16 in Wallace and Snedecor.
These correlations are all highly significant. While both breed and sex are found to be associated with differences in heart rate, these relations are possibly to be conceived . •
y42i :6-.06£ X
^•
' ..
>s
. *£00
2P00 2200 2.400 2SOO LIVE WEIGHT '(GRAMS)
2300
3,000 1200
FIG. 2. Relationship of heart rates per minute and live weight for Rhode Island Red and Single Comb White Leghorn hens and cocks.
as secondary to a more general relation between body weight and heart rate. The small White Leghorn females have the fastest rate and the large Rhode Island Red males have the slowest rate. The Rhode Island Red females and the White Leghorn males of somewhat similar body weight have about the same heart rate. The relation between body weight and heart rate has been plotted in Figure 2. The line of regression has been calculated by the method of least squares and has been found
270
E. H. MCNALLY
to be 422.6 - 0.06SX DISCUSSION The increase in heart rate with a decrease in body size has already been pointed out for different species of birds and mammals by Buchanan (1910) and Clark (1927). When the heart rate of the fowl is compared with that of other species it is found to be much faster than would be expected for a bird of its body weight. The percentTABLE 6.-
-Percentage heart weight and heart rate of certain mammals and birds*
Type of animal
Percentage heart weight of body weight*
Heart beats per minute*
0.59 0.75 0.45
70 120 160
1.36 1.5 0.63 0.35
800 185 240 261
Mammals: Medium-sized dog. . . Birds: Sparrow Pigeon Duck (tame) Fowl (R.I.R.)
* Compiled and modified from Buchanan's (1910) data, except R.I.R. fowl.
age of heart weight to body weight, and rate of metabolism in relation to body weight are complicating factors that may under certain conditions give smaller birds a slower or more rapid heart rate. The rapid heart rate of the fowl would appear to be partially due to the small percentage heart weight. Comparative figures for the percentage heart weight and heart rate of different species of animals are given in Table 6. In these data the rapid heart rate and the remarkably small percentage heart weight of the fowl are well displayed. The small weight of the heart of the domestic fowl seems to be a characteristic of domestic animals in general. The Rhode Island Reds used in our experiment had remarkably
small hearts. Buchanan (1910) states: "The relatively small heart of animals kept for food, such as the hen, the tame duck, the pig, the ox, and the cow is on the other hand a consequence of the artificial fattening up of these animals, thus increasing their body weight, while their hearts, having little to do, do not keep pace, it being possible to supply the oxygen demanded by increasing the frequency of beat." Clark (1927) also pointed out that active animals capable of severe and continued exertion have a higher percentage heart weight than inactive animals. SUMMARY
Observations were made on the heart rates of 12 Rhode Island Reds and 12 Single Comb White Leghorns, 6 males and 6 females of each breed, using the electrocardiotachometer of Horton. The average heart rate for all the birds of both breeds and sexes was found to be 282 beats per minute during the day, ranging from a low of 192 in a Rhode Island Red male to a high of 396 in a White Leghorn female. In longtime observations a minimum heart rate was found during the early morning (1 to 3 a.m.), as low as 160 beats per minute being recorded in Rhode Island Red males. A correlation holds between body weight and heart rate which appears to be more fundamental than either breed or sex differences in the two breeds studied, heavier birds showing a slower heart rate. The heart weight-body weight ratio calculated for the Rhode Island Red birds was observed to be lower than that reported for any other wild or domestic bird. REFERENCES
Boas, E. P., and E. F. Goldsmidt, 1932. The heart rate. C. C Thomas, Pub., Baltimore. Boas, E. P., and W. Landauer, 1933. The effect of elevated metabolism on the heart of frizzle fowl. Amer. Jour. Med. Sci. NS. 185:654.
HEART RATE OF THE DOMESTIC FOWL Bogue, J. Y., 1932. The heart rate of the developing chick. J. Exp. Biol. 9:351. , 1933. The electrocardiogram of the developing chick. J. Exp. Biol. 10:286. Buchanan, F., 1910. Significance of the pulse rate in vertebrate animals. Ann. Rpt. Smithsonian Inst., p. 484. Clark, A. J., 1927. Comparative physiology of the heart. Cambridge Univ. Press. Fronda, F. M., 1925. Some observations on the body temperature of poultry. Cornell Vet. IS :8-20.
271
Horton, J. W., 1938. An electronic cardiotachometer. Electronics, Aug. 1938. Stiibel, H. S., 1910. Beitrage zur Kenntnis der Physiologie des Blutkreislaufes bei verschiedenen Vogelarten. Pfluger's Arch, f .d. ges Physiol. 13S :249. Wallace, H. A., and George W. Snedecor, 1931. Correlation and Machine Calculation Rev. Iowa State College of Agriculture. Winchester, C. F., 1940. Seasonal, metabolic, and endocrine rhythms in the domestic fowl. Missouri Agri. Sta. Res. Bull. 315.