76 THE GROWTH OF THE BRAIN. 



is at least plausible that in these cases a premature 

 growth of the brain has been one factor in causing 

 death. 



These facts can perhaps be taken as examples of the 

 danger attending the deviation from the mean in the 

 construction of a body, for in the case of the brain, as 

 in that of any other organ or system, undue development 

 weakens the entire individual, and so the facts derived 

 from necropsies are to be applied to the history of living 

 individuals only after proper correction. In connection 

 with this last point the mortality records may be cited. 

 Observations have shown that the percentage of deaths 

 in the population at large varies with age, being high 

 in the first years of childhood and in old age, and low 

 in the middle years. These relations are expressed in 

 Fig. 14. 



The curve just given needs perhaps a word of explana- 

 tion. It was developed by Hensen on the basis of 

 Bockh's tables of mortality, which tables depended on 

 Prussian statistics for the years 1 865-6. T The tables are 

 based on the assumption of a population of one million 

 individuals, of the various ages from o to 100 years. 

 The number of deaths occurring among those of a 

 given age is represented as a percentage. The portion 

 of the curve before o years represents the percentage 

 of prematurely still-born children. It is easy to see 

 that, while the rate of mortality at birth is very high 

 indeed, it rapidly sinks until about the fifth year, 

 when it has fallen to the neighbourhood of I per cent. 

 From this age it rises slowly for the next sixty years, 

 and finally very rapidly. An explanation of this is to 

 be found by considering both how the body is built up 

 and how it breaks down. 



That the body is a house is a simile coming down to 

 1 Hensen, Hermann's Handbuch der Physiologic, 1881. 



