583 GENERAL REVIEW OF THE NUTRITIVE FUNCTIONS. 



each of the three summer months being 80,J;hat of January is nearly 140, and 

 the average of February and March is 125. This is confirmed by the result 

 obtained by MM. Villerme and Milne-Edwards in their researches on the mor- 

 tality of the children conveyed to the Foundling Hospitals in the different 

 towns in France ; for they not only ascertained that the mortality is much the 

 greatest during the first three months in the year, but also that it varies in dif- 

 ferent parts of the kingdom, according to the relative severity of the winter. 

 As childhood advances, however, the winter mortality diminishes, whilst that 

 of the spring undergoes an increase ; this is probably due to the greater preva- 

 lence of certain epidemics at the latter season ; for the same condition is 

 observed, in a still more remarkable degree, between the ages of 8 and 12 

 years, the time when children are most severely affected by such epidemics. 

 As the constitution requires greater vigour, and the bodily structure attains its 

 full development, the influence of the season upon mortality becomes less appa- 

 rent ; so that, at the age of from 25 to 30 years, the difference between the 

 summer and winter mortality is very slight. This difference reappears, how- 

 ever, in a very marked degree, at a later period, when the general vigour, and 

 the calorifying power, undergo a gradual diminution. Between the ages of 

 50 and 65 it is nearly as great as in early infancy ; and it gradually becomes 

 more striking, until, at the age of 90 and upwards, the deaths in January are 

 158 for every 64 in July (a proportion of 2 to 1) ; and the average of the 

 three winter months is 145, whilst that of the three summer months is only 

 68, or less than one-half. 



729. Not only does the same individual possess different degrees of calori- 

 fying power, at different periods of his life ; but also at different parts of the 

 year. Dr. Edwards found that Sparrows, when exposed for some time to a 

 temperature of 32 during the summer, rapidly lost heat, the refrigeration 

 during 3 hours being from 6 to 21 degrees; but that, when they were placed 

 in the same circumstances during winter (after having been accustomed to a 

 warm temperature), the refrigeration was much less, not being in any instance 

 more than 2 in 3 hours. Although it would be difficult to prove the fact 

 experimentally in regard to Man, there can be little doubt that he shares with 

 the other Mammalia in this variation. It is well known that the general 

 vigour of the system is less in summer than in winter ; in hot climates, than 

 in moderately cold. Moreover, we continually experience the great discom- 

 forts of a cold day in summer; when, our system not being prepared for it, 

 we can less readily maintain our temperature at its normal standard. The 

 practical inference, that we should be much on our guard against exposure 

 to low temperatures during summer, is one of much importance ; and its 

 value has been fully confirmed by experience. The same principle may also 

 be applied to the explanation of the well-known fact, that those who have been 

 long resident in warm climates feel the cold acutely ; whilst those who have 

 been inured to cold are able to resist it much better than those who are exposed 

 to it for the first time. The former have a continued summer constitution ; 

 and their system not being called upon by its external conditions to produce 

 much heat, the power is after a time partially lost. On the other hand, those 

 who live in cold climates have a perpetual winter constitution (as it were) 

 established ; and the amount of heat generated by them is much greater. It 

 will be obvious that this must be the case, if Man's capability of living under 

 the greatest varieties of climate be sufficiently considered. From Dr. E.'s 

 experiments it appears, that every month makes an evident difference in the 

 seasonal degree ; the heat lost by Sparrows in August being much less than 

 that lost by birds of the same species in July. 



730. Our knowledge of the dependence of all the vital processes in warm- 

 blooded animals, upon the Heat of their bodies, and of the dependence of 



