160 REPORT — 1855. 



On the Physiological Law of Mortality, and on certain Deviations from it, 

 observed about the Commencement of Adult Life. By Prof, A. Buchanan, 

 M.D., University of Glasgow. 



I. The object of the first part of this memoir was to determine the normal course 

 of mortality as affected by age alone, without reference to other circumstances. 



What we name the law of mortality is not a simple law, but a compendious ex- 

 pression, by which we denote the operation of various laws, physiological, physical, 

 and moral. Of these, the physiological laws are so uniform in their operation, that 

 they impress certain characteristic features upon the law of mortality, according to 

 age, which are observed amidst all the diversities which it exhibits under varying 

 circumstances, physical and moral. 



Of the physiological laws subordinate to the general law of mortality, the principal 

 by far is the law of natural decay, which regulates not the human organism alone, 

 but every organism, animal and vegetable, fixing the limits of its period of existence. 

 This law must not be supposed to operate only in cases of extreme old age. Every 

 child at birth contains within it the elements of its own decay ; so, that although 

 placed in the most favourable external circumstances, and exempted from all noxious 

 influences, the series of organic actions in which life consists would come sponta- 

 neously to a termination ; and this takes place at all ages, as we infer from seeing 

 health decline, and a fatal disease declare itself, without the intervention of any ex- 

 ternal cause known to be hostile to human life. 



The law of infantile mortality, again, depends upon causes of a different kind. 

 The principal of these is the transition from uterine to independent life, which occa- 

 sions a great change in all the actions of the bodily organs, and in the conditions 

 and circumstances in which they are carried on ; whence many infants perish in the 

 transition, from the conditions necessary to the former mode of life being interrupted, 

 while those necessary to the latter are not established with sufficient promptitude, 

 or only imperfectly established. At a later period the mortality is kept up by the 

 delicacy and vascularity of the tissues, the great excitability of the nervous system, 

 now first exposed to irritation, the great size of the head, and the unequal develop- 

 ment of other organs. 



The mortality of early infancy is exactly similar in kind to the mortality (if that 

 name can be applied to the destruction of embryonic life) attendant on the transition 

 from ovarian to intro-uterine life, when a still more complete revolution takes place 

 in all the actions of the system, and a new series of relations to the maternal organs 

 is established. The destruction of life which ensues is greatest at first, and gradually 

 diminishes as the new adaptations are effected. 



To these physiological laws the uniformity in the course of mortality correspond- 

 ing to age is to be ascribed; for whatever deviations occur in different communities 

 from a difference in external circumstances, the general direction is the same in all, 

 marked by a great excess of deaths, gradually decreasing, in early life ; a similar 

 excess, gradually increasing, in advanced life ; and a comparatively low rate of mor- 

 tality in the intermediate period. 



Of the external causes which occasion the diversities in the law of mortality in 

 different communities, there are some which may be named conspiring causes, as they 

 act in conjunction with the physiological causes above-mentioned, and magnify their 

 effects ; while there are others of an interfering kind, that disturb the physiological 

 results. To the latter class belong those causes that operate solely, or with peculiar 

 intensity, at certain periods of life. Thus, a war occasions devastation among the 

 young and strong, and disturbs the normal course of mortality. Causes, again, which 

 operate more equably at all ages are of the conspiring class, for the physiological 

 state of the body, varying with age, assists or resists their action. Thus the ex- 

 tremes of temperature tell chiefly on the infirm bodies of the young and old, while 

 persons in the vigour of life resist their influence. 



Of the law of mortality resulting from these causes, as it is observed in England, 

 the most prominent characters may be expressed in general terms by saying, that 

 human life is most secure at 13 years of age, and that as it recedes from that point 

 towards either term of existence, it becomes less secure in a ratio which is constantly 

 increasing. 



