INTRODUCTIOJC xxi 



birds are hot-blooded creatures; indeed, their 

 blood is much warmer than that of mammals, the 

 temperature ranging from 100° to 112°. The highest 

 figure is attained by the smaller perching birds, such 

 as Finches; Hawks do not maintain a temperature 

 above 109°, and Gulls only a little above 104°. 



This rise in the temperature of the blood is due to 

 several causes too technical to be here discussed. But 

 chief among them is the fact that the heart of the bird, 

 like that of the mammal, is a four-chambered heart, 

 whereby a more perfect oxidation of the blood is pos- 

 sible than is the case with reptiles, in which the 

 heart has but three chambers. And for this reason: 

 When passed through a four-chambered heart, the 

 impure blood brought back from the body to the right 

 side of the heart is driven through the lungs to be 

 thoroughly purified by the air drawn in during breath- 

 ing; it is then received by the left side of the heart, 

 thence to be sent over the body without any mingling 

 of the two streams. In the reptile this mingling takes 

 place, and consequently a smaller relative quantity 

 of the heat-giving oxygen is brought into the system. 

 But, strangely enough, the blood of reptiles and 

 birds agree in this, that the little red bodies, or "cor- 

 puscles," whose duty it is to absorb the air from the 

 lungs and the carbonic acid from the tissues of the 

 body, have each a central "kernel," or nucleus, whereas 

 the blood-corpuscles of mammals h3,ve no such nu- 

 cleus. 



To expand further this matter of the temperature 

 of the blood a somewhat intimate knowledge of physi- 

 ology and chemistry would be required in the reader. 



