348 OF NUTRITION. 



and there is a gradual diminution in the stature and bulk of the body, 

 and in its physical powers. All the functions are performed with de- 

 creased energy ; and the comparative inertness of the nutritive processes 

 is seen in the difficulty with which the effects of severe injuries are 

 repaired, in the length of time requisite for the purpose, and frequently 

 in the imperfection of the result. 



622. During the successive periods of life, there are many remarkable 

 changes in the relative nutrition of different organs ; which we can attri- 

 bute to nothing else, than to inherent differences in their own powers of 

 development. Thus, during the early stages of foetal existence, the 

 greatest energy of growth is seen in certain parts which are to answer 

 but a temporary purpose, and which are afterwards completely atrophied. 

 This is the case, for example, with the Corpora Wolffiana, which seems 

 to answer the purpose of temporary kidneys, and in connexion with 

 which the permanent kidneys and the genital organs are developed ; and 

 of these bodies, though of large size in the early embryo, and evidently 

 of great importance, no trace whatever is afterwards to be discovered. 

 So in regard to the Supra-Renal capsules, the Thymus and Thyroid 

 glands, and other organs, we find their proportional size the greatest, 

 and their function evidently the most active, during foetal existence and 

 in early infancy ; after which their bulk diminishes in proportion to the 

 rest of the body, and their functional activity seems almost at an end. 



623. Even in the relative development of the organs which form 

 essential parts of the permanent structure, we find considerable varia- 

 tions at different periods of life. Thus the evolution of the generative 

 system does not usually take place, until the rest of the body is 

 approaching its maturity ; but cases sometimes occur, in which this 

 apparatus attains its full development, both in the male and the female, 

 at a very early period of childhood, and seems capable of performing 

 its functions. In the Human species, these organs, when once evolved, 

 remain always in a state of preparation for the performance of their 

 function, unless they are atrophied through complete disuse, or have 

 lost their vigour by age, or through excessive demands upon their acti- 

 vity ; but in most of the lower animals, the development of these organs 

 is periodical through the whole of life, taking place at a certain season 

 of the year, and being greatly influenced, it would appear, by the 

 external temperature, and by the supply of food. Thus in the Sparrow, 

 the testes are no larger than mustard-seeds, during the greater part of the 

 year ; but in the spring, they acquire the size of large peas, and it is 

 then only that they possess any procreative power. 



624. We are not always to judge of the degree of development of 

 organs, however, by their size alone ; for the completeness of their struc- 

 ture, and their aptitude for the performance of their functions, must 

 also be taken into the account. Thus in the new-born infant, the organs 

 of Digestion and Assimilation, though of small size, are so completely 

 formed as to be able at once to take on the duty of receiving and pre- 

 paring the nutritive materials, provided these are supplied in a form 

 adapted to their powers ; the Circulating apparatus is fully adequate to 

 transmit the products of the action of those organs to the body in 

 general, and to bring back the results of its continual decay ; and the 



