RESPIRA TION. 533 



separated from the preceding and succeeding groups by a variable interval, 

 usually 30 to 45 seconds. This form of respiration is frequently observed in 

 uraemia, after severe hemorrhage, and in certain diseases of the heart and brain. 

 Periodical alterations in the respiratory rhythm may be observed in the last 

 stages of asphyxia, in poisoning by chloral, opium, curare, and digitalis, in cer- 

 tain septic fevers, in certain animals during hybernation, etc. In the human 

 organism, excepting during sleep and in the aged and the very young, such 

 non-rhythmical respirations are always indicative of abnormal conditions. 



In warm-blooded animals the movements are generally of a much more 

 rhythmical character than in cold-blooded animals. 



The Frequency and Depth of the Respiratory Movements. The 

 respiratory rate is affected by a number of conditions, chiefly species, age, 

 posture, time of day, digestion, activity, internal and external temperature, 

 season, barometric pressure, emotions, the composition of the air, the composi- 

 tion of the blood, the state of the respiratory centres and nerves, etc. 



The following figures, compiled from various sources, indicate the wide 

 differences in various species, the rates being per minute : 



Horse 6-10 



Ox 10-15 



Sheep 12-20 



Pig 15-20 



Man 16-24 



Cat . 20-30 



Dog 15-25 Pigeon 30 



Kabbit .... 50-60 



Sparrow ... 90 



Guinea-pig . . 100-150 



Eat . . 100-200 



The average rate in man varies according to different investigators, from 

 11.9 by Vierordt to 19.35 by Ruef. Hutchinson noted 16-24 per minute as 

 a mean of 2000 observations. There is a general, but not an absolute, rela- 

 tionship between the rate and the size of the body, as regards both different 

 species and different individuals of the same species : as a rule, the smaller the 

 species the more frequent the respirations; the same holding good for indi- 

 viduals of the same species. 



The marked influence of age is illustrated by the records of the observa- 

 tions by Quetelet on 300 individuals : 



Rate per Minute. 



Age. Maximum. Minimum. Mean. 



New-born 70 23 44 



1- 5 years 32 . . 26 



15-20 " 24 16 20 



20-25 " 24 14 18.7 



25-30 " 21 15 16 



30-50 " 23 11 18.1 



Posture exerts a marked influence, especially in those enfeebled by disease. 

 Guy records, in normal individuals, 13 while lying, 19 while sitting, and 22 

 while standing. 



The diurnal changes are in close accord with those of the pulse-rate (p. 41 2). 

 The rate is less frequent by about one-fourth during the night than during the 

 day, and more frequent after meals, especially after the mid-day meal. Vier- 

 ordt noted the following variations: 9 A.M., 12.1; 12 M., 11.5; 2 P.M., 13; 



