AGE. 



67 



the phenomena of disease. An examination 

 of the textural properties of the two sets of 

 vessels leads to the same conclusion. Sir 

 Clifton Wintringham, in his Experimental 

 Enquiry, fully demonstrated that the venous 

 coats in the young animal far exceed the 

 arterial in density, and that, consequently, 

 they are less subject to distension. When 

 maturity is attained, the disproportion between 

 the resistances of these vessels no longer 

 exists. 



However well provided the infant may be 

 with the mechanical apparatus of pores and 

 vessels, these can be of no avail unless the 

 fluid they contain possesses certain chemical 

 properties. Now the blood in early extra- 

 uterine life presents the same general characters 

 as in more advanced periods ; but there is yet 

 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 

 periods have not been defined by experiment, 

 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, 

 complete in its functions. Its volume, how- 

 ever, is large in proportion to the size of the 

 body. Its parietes are less firm in texture, 

 and of a paler colour than they afterwards 

 become ; but their contractility is more active. 

 The pulsations are from 120 to 140 in a 

 minute. The large volume is in harmony 

 with the quantity of the fluid, the comparative 

 weakness of its parietes with the small extent to 

 which their impulse requires to be propagated, 

 and with the trifling resistance ; and the quick 

 successions of its contractions furnish the fresh 

 supplies of the nutriment required by the 

 energy of growth. In the progressive develop- 

 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 

 of the circulating fluid ; the fibres become 

 stronger and of a deeper hue, so that the 

 contractions are more capable of propelling 

 the blood through the greater extent which it 

 has now to traverse, or, more strictly speaking, 

 of communicating a shock to a greater column; 

 but the pulsations are slower, agreeably to the 

 diminished requirements on the part of the 

 capillary actions. We must not omit to ob- 

 serve that at birth the parietes of the left 

 ventricle scarcely exceed those of the right in 

 thickness; but from this period an alteration 



* De Blainville states, on the authority of 

 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 

 smaller proportion than in succeeding periods. Cours 

 de Physiologie, t. ii. p. 262. 



commences, and rapidly proceeds until the 

 thickness of the latter is to that of the former 

 as 1:4. This change corresponds with the 

 closure of the foramen ovale, the obliteration 

 of the ductus arteriosus, and the consequent 

 execution of the systemic circulation by the 

 left ventricle only. The relative capacities of 

 the right and left cavities begin to alter soon 

 after birth. From tables given by Meckel it 

 appears that, while at birth the capacity of the 

 former compared with that of the latter is as 

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



The lungs at the moment of birth undergo 

 a more remarkable alteration in their form, 

 their texture, and their contents, than any 

 other organ in the system ; but during infancy 

 and childhood they present no appreciable 

 change in their organization, although a change 

 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- 

 wards; and practical observations of the highest 

 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- 

 quency is a necessary accommodation to the 

 rapidity of the circulation. At puberty there 

 is a marked development of the organs of 

 respiration ; the volume of the lungs increases 

 in conformity with the expansion of the thorax; 

 while the greater determination of the blood 

 to their vessels is indicated by the deeper hue 

 of the parenchyma, by the liability to pulmo- 

 nary hemorrhage, so characteristic of this 

 period, and perhaps also by certain diseases 

 which affect the nutrition of these organs. 

 The corresponding activity of function is indi- 

 cated by the increased power of calorification, 

 the energy of muscular motion, and the exalta- 

 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, 

 though somewhat more remote, with the pul- 

 monary development. 



We pass from the system which imparts 

 new properties to the blood to that which 

 supplies it with nutriment. No imperfection 

 is discoverable in the apparatus of digestion 

 in the new-born infant ; every organ is com- 

 plete as an organ, but passes through va- 

 rious changes in adaptation on the one hand 

 to the food that is supplied, and to the mode 

 of receiving it, and on the other hand to the 

 demands of the other parts of the body. The 

 organs employed in conveying and modifying 

 the chyle, viz. the lacteals and the mesenteric 



* Manuel d'Anat. t. ii. p. 284. 

 t On the Influence of Physical Agents, &c. 

 translated by Drs. Hodgkin and Fisher. 



F 2 



