492 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



demands made upon it for oxygen, potentially or actually, could meet 

 with only imperfect success. 



Let us now see in how far the hearts of birds and mammals, having 

 the power to regulate the oxygen supply by regulating the volume 

 of blood expelled in unit time, succeed in doing so when it is asked 

 of them. As a measure of the rate at which oxygen is consumed in 

 the different animals we may take either the oxygen intake or the 

 carbon-dioxide output of a unit of weight in unit time, as the two 

 things run roughly parallel. In the two following tables the carbon- 

 dioxide output is given because it happens to be known for a larger 

 number of species than the oxygen intake. The numbers are for the 

 most part taken from the table in Pembrey's article on " Chemistry 

 of Respiration " in Schafers Textbook of Physiology and represent 

 the average in round numbers when several results are there given 

 by different observers. Those for birds which are not to be found 

 there are determinations kindly made for me by Mr. C. G. Douglas, 

 fellow of St. John's College, Oxford. 1 The pulse rates of all the 

 birds and of the smaller mammals have been determined b} T myself 

 in a manner to be described immediately; those of the larger mam- 

 mals have been taken on textbook authority when none other was 

 available. As a measure of the volume of blood expelled per beat the 

 weight of the heart in percentage of the body weight has been taken. 

 This has been determined for a large number of birds by Parrot (3), 

 but unfortunately not for many of which the pulse rates are known. 

 For most of these, as well as for the mouse, I have determined it 

 myself. For most of the other mammals mentioned it has been de- 

 termined by Bergmann (8), but the results of his observations are 

 referred to, together with some more determinations of his own and 

 those of a few other people for other mammals, by Joseph (9). 

 Unfortunately the number of individuals from which the " average," 

 either of pulse rate or of relative heart weight, is taken was usually 

 small and sometimes (in all the cases marked with an asterisk) the 

 data were only ascertained from a single individual of a species; as 

 we know that in other species there is a good deal of individual varia- 

 tion, the numbers given in these columns may not hereafter be found 

 to be the correct averages. They probably are so, however, in the 

 case of man and rabbit, in which they have already been ascer- 

 tained from large numbers of individuals. It is, of course, highl}' 

 desirable that the correct average should be known for every case, 

 but it is difficult to get people to make large collections of facts, and 

 it is debatable in how far their doing so is a thing to be encouraged, 

 so long as the interest attaching to them is not in evidence. The fol- 



1 For each bird he determined also the oxygen intake ; since this datum for the canary 

 and for the tame duck has not yet been put on record, this occasion may be used for 

 stating that it was found to be 10.99 and 1.66 grams per kilo per hour, respectively, for 

 the two birds. The canary was remarkably quiet all the time it was under observation. 



