AGE. 





the phenomena of disease. An examination commences, and rapidly proceeds until the 

 of the textural properties of the two sets of thickness of the latter is to that of the former 

 vessels leads to the same conclusion. Sir as 1:4. This change corresponds with the 

 Chfton Wintringham, in his Experimental closure of the foramen ovale, tin- <>llit< ration 

 Enquiry, fully demonstrated that the venous of the ductus arteriosus, and the consequ. nt 

 coats in the young animal far exceed the execution of the systemic circulation by the 

 arterial in density, and that, consequently, left ventricle only. The relative capacitV 

 they are less subject to distension. When the right and left cavities begin to 

 maturity is attained, the disproportion between after birth. From tables given by M< : 



longer appears that, while at birth the capacity of the 

 former compared with that of the latter is as 

 1 : 1$, at the age of 50 it is nearly 3:1.* 



The lungs at the moment of birth undergo 



vessels, these can be of no avail unless the a more remarkable alteration in their form, 

 fluid they contain possesses certain chemical their texture, and their contents, than any 

 properties. Now the blood in early extra- other organ in the system ; but during infancy 

 uterine life presents the same general characters and childhood they present no appreciable 

 as in more advanced periods ; but there is yet change in their organization, although a change 



no 



the resistances of these vessels 

 exists. 



However well provided the infant may be 

 with the mechanical apparatus of pores and 



wanting a comparative analysis of this fluid 

 at different ages.* Inferentially we can enter- 

 tain no doubt that it is fully adapted to the 

 purposes of nutrition, when we consider the 

 conditions of the chylifactive and respiratory 

 functions, and that, although the differences 

 of its composition in early and in more mature 



must be inferred from the increase of their 

 function. In infancy there is a smaller con- 

 sumption of oxygen ; and the power of gene- 

 rating heat, a function so intimately connected 

 with respiration, is inferior to that possessed 

 in later periods. Much light has been thrown 

 on this subject by the researches of Dr. Ed- 



periods have not been denned by experiment, wards; and practical observations of the highest 



they must bear a relation to the different de- 

 grees of nutrition and secretion. The differ- 

 ence, however, between the blood of the infant 

 and that of the aged is perceptible to the 

 senses, and will be noticed hereafter. 



Pursuing the channels of the blood to the 

 heart, we find this organ, as stated above, 



mportance in the management of infants, 

 founded upon the facts which he has ascer- 

 tained, are to be met with in his valuable 

 work.f The inspirations and expirations are 

 more frequent at this early period, although 

 the chemical actions between the air and the 

 blood are less considerable. This greater fre- 



complete in its functions. Its volume, how- quency is a necessary accommodation to the 



ever, is large in proportion to the size of the rapidity of the circulation. At puberty there 



body. Its parietes are less firm in texture, is a marked development of the organs of 



and of a paler colour than they afterwards respiration ; the volume of the lungs increases 



become ; but their contractility is more active, in conformity with the expansion of the thorax; 



The pulsations are from 120 to 140 in a 

 minute. The large volume is in harmony 



while the greater determination of the blood 

 to their vessels is indicated by the deeper hue 



with the quantity of the fluid, the comparative of the parenchyma, by the liability to pulmo- 

 weakness of its parietes with the small extent to nary hemorrhage, so characteristic of this 

 which their impulse requires to be propagated, period, and perhaps also by certain diseases 

 and with the trifling resistance ; and the quick which affect the nutrition of these organs. 

 successions of its contractions furnish the fresh The corresponding activity of function is null- 

 supplies of the nutriment required by the cated by the increased power of calorification, 

 energy of growth. In the progressive develop- the energy of muscular motion, and the exalta- 



ment of this organ we notice that the bulk, 

 although increasing so long as general growth 

 continues, is proportionately smaller, a cir- 

 cumstance that corresponds with the diminution 



tion of the cerebral actions; functions well 

 known to have a direct relation with that of 

 respiration ; while the establishment of the 

 generative faculty appears to own a connexion, 



of the circulating fluid ; the fibres become though somewhat more remote, with the pul- 



stronger and of a deeper hue, so that the 

 contractions are more capable of propelling 



monary development. 



We pass from the system which imparts 



v^wii 1. 1 a,VsiiwLio cue niv/ic* Vsu.ijci.uii' \Ji |*v|/v*au v j; . , -. . , 



the blood through the greater extent which it new properties to the blood to tn; 



has now to traverse, or, more strictly speaking, supplies it with nutriment. No imper 



of communicating a shock to a greater column; is discoverable in the apparatus < 



but the pulsations are slower, agreeably to the in the new-born infant ; every 01 



diminished requirements on the part of the plete as an organ but passes throi 



capillary actions. We must not omit to ob- rious changes in adaptation on the . 



serve that at birth the parietes of the left to the food that is supplied, and to the mode 



ventricle scarcely exceed those of the right in of receiving it, and on the other hand tn the 

 thickness; but from this period an alteration demands of the other parts of the t ody. Ih 



organs employed in conveying and modifying 



* De Blainville states, on the authority of the chyle, viz. the lacteals and the mesent 

 Fourcroy, that in infancy the albumen of the blood 

 is more abundant, that the fibrin is softer and 



more gelatinous, and that the phosphates are in 



-- J - Cours 



de Physiologic, t. ii. p. 262. 



* Manuel d A aat. t. 



translated by 



p. 284. 



&c. 



