400 



BIRD. 



chantet of the inductive results of our observation 

 of birds without an appendix of exceptions of still 

 greater length. 



But, though we must receive it with exceptions and 

 limitations, there is still observable in birds, accord- 

 ing as they depart in their general characters from 

 the rapacious ones, an increase of seasonal change, 

 connected with that energy, which is awakened at 

 the pairing time ; and though the individual charac- 

 ters of this change vary exceedingly, there are two 

 great and not very badly marked divisions of it, the 

 one taking place in those birds which are more vege- 

 table in their feeding, and the other in those that 

 i'eed more upon insects. In the former, it displays 

 itself in greater brilliancy of plumage, and more 

 intensity of action generally, especially in the male 

 birds; under the latter it displays itself more in 

 change of place. Not a little of the character of 

 birds, both in themselves, and also as they are by 

 analogy (which they are largely and accurately), 

 indices to the rest of nature, might be worked out 

 upon this principle ; but, even though the length of 

 this article did not threaten to exceed all wonted 

 bounds, in treating on the same subject, this is not 

 exactly the place Tor it. We still want the elements, 

 in the accounts of the modifications of character by 

 the feet and the wings, and also of the bill, as the 

 grand prehensile organ in the feeding system ; ami 

 therefore we must defer the general conclusions till 

 we come to the articles on CHANGE OF PLUMAGE, 

 MIGRATION, and PAIRING. We shall therefore only 

 further remark, in passing, that much of the character 

 of the different tribes depends on the varied deve- 

 lopment of this seasonal energy ; and that the cha- 

 racter thus produced is much modified, according as 

 the energy is more marked off in the locality which 

 the bird inhabits when it is at first exerted, or 

 prompts it to migration to a distant region. 



The systems of circulation and respiration, in birds 

 as in other animals, are closely connected, though not 

 so much so as in the mammalia. The circulation in 

 both is performed by means of a double heart, con- 

 sisting of two ventricles for propelling the blood, and 

 two auricles for receiving that fluid on its return ; 

 and connected with these, as in all animals that have 

 the heart double, there are two sets both of arteries 

 and of veins, a pulmonary set arid a systematic one. 

 The circulation is, as has been hinted already, more 

 rapid in birds than in the mammalia, which agrees 

 with the greater violence and longer continuance of 

 some of their actions. But though these more violent 

 actions, such as coursing on two feet as fleetly as 

 antelopes do on four and with the aid of the flexible 

 spine and its muscles, as in the ostrich, plunging into 

 the water like the gannet or the cormorant, dashing 

 through that element like the divers, cleaving the air 

 beyond comparison with all terrestrial speed, as in 

 the plovers, the swift, or the pratincole, or breasting 

 the tempest with the majesty of the eagle, require, 

 and are furnished with a supply of blood, proportional 

 to the waste which their great energy must occasion ; 

 yet they are by no means so well suited to an equally 

 rapid breathing by means of lungs. But the applica- 

 tion of renovating air to the blood must, in all animals, 

 be proportional to the circulation ; and, among ver- 

 tebrated animals, it is only the reptiles and fishes 

 which have the temperature low and the circulation 

 lagging, and which spend much of their time in a 

 state of comparative inaction, that can carry on their 



systems in a healthy state with only a partial aeraiion 

 of the blood. 



If the subject is considered according to onr plans 

 in contriving and executing, there is thus a difficulty 

 to be overcome in the case of the birds, similar to 

 which nothing occurs in that of any of the other ver- 

 tebrated animals. They stand more in need of the 

 action of the air than any other animals ; and their 

 habits are tuch that they are less able to bear even 

 the same action, by means of the ordinary apparatus 

 of lungs. 



Now this is one of those difficulties which human 

 wisdom could never see the means of overcoming, 

 except in the accomplishment of the very object, the 

 means of accomplishing which are the subject ot 

 inquiry ; and therefore it is wholly above the reach 

 of the human powers, and in itself a perfect demon- 

 stration that the works of creation must have origi- 

 [ nated from One omniscient in knowledge, as well as 

 omnipotent in action. But though in this, as in all 

 other cases, we could never have fathomed the pur- 

 pose of the Eternal, without (he example which he 

 lias set, yet the lesson held forth in that example is, 

 when scanned with even a moderate degree of atten- 

 tion (a degree of which any human being is compe- 

 tent), is so plain and simple, that a child mav under- 

 stand it. It is the same with all nature ; and if the 

 vain affectation of superior wisdom on the part of 

 those who have attempted to school us in it, had not 

 encumbered and concealed it by the clouds and dark- 

 ness of words and wayward theories, the learned 

 and the unlearned might read this, the elder and 

 more general volume of " The book of the living 

 God," together, and with nearly the same pleasure 

 and the same profit. 



And the means by which the action of the air on 

 the blood of birds is rendered equal to the rapidity 

 in circulation, and consequent necessity of vital repair, 

 in that fluid, without the painful fatigue of ever punt- 

 ing lungs, is made, like all other contrivances in 

 nature, to answer other important purposes at the 

 same time. The lungs of birds are ample in their 

 dimensions, and have the cells into which air is 

 admitted larger than in the mammalia ; and they are 

 kept in their places by being fastened to the bones. 

 Ramifications extend from them in tubes and cells 

 through the whole cavity of the body, into the hol- 

 lows of the bones, and in short, along the course of 

 every artery which is not immediately imbedded in 

 those muscles, which are in action during the violent 

 exertions of the bird. The blood-vessels in these 

 muscles are fewer than those in the muscles of the 

 mammalia, as any one may infer from the greater 

 rigidity of their texture, and the whiteness of their 

 colour. Thus, there is not a blood-vessel of any con- 

 siderable size in the whole body of a bird, to the 

 coats of which the air has not access during the 

 greater part of their course ; and thus the real action 

 of breathing in birds is not concentrated into one 

 organ, to be toiling and panting there, as it would be 

 in the lungs of the mammalia, but distributed over 

 the whole circulation, and consequently diminished 

 in local intensity, in proportion as it is extended over 

 a greater surface. 



This is a subject which it is impossible to bring to 

 the test of numbers, so as to compare accurately the 

 diminution of local action by means of the general 

 access of air to the blood-vessels. There arc two 

 difficulties, neither of which can be, from the great 



