266 THE CAUSATION OF DISEASE. 



morbidly to certain mal-E's, such, for instance, as those just 

 mentioned, not by virtue of any specific state of the tissue 

 peculiar to this child or that, but in consequence of a condition 

 of body belonging to the whole race at that time of life. If, 

 therefore, we were to take the mortality of children as a measure 

 of the extent to which special morbid tendencies are inherited, 

 we should be erring, owing to the fact that children, as a class, 

 are peculiarly susceptible to certain morbid influences, and to 

 the further fact that they are freely exposed to these influences. 

 I have purposely made no mention, hitherto, of the zymotic 

 fevers. Is the excessive frequency with which children suffer 

 from these zymotic fevers due to a peculiar susceptibility on 

 their part, or to the fact that they are more exposed to a first 

 attack of the poison than adults ? It is probable that children 

 are, on the whole, more prone to be affected by them than 

 adults ; but the chief reason of the greater frequency of the 

 specific fevers during childhood is undoubtedly that one attack 

 confers immunity from another, and that the great majority 

 of adults have already been exposed to the poisons. 



A further source of error is the fact that the longer an indi- 

 vidual lives, the greater is the quantity of mal-E to which he 

 is exposed. So that, other things being equal, the mortality 

 would increase with each successive year. 



In order to estimate properly the mortality at the several 

 periods of life from disease due to inherited specific structural 

 weakness, it would be necessary to expose an entire community 

 to an average healthy E, and then, making due allowance for 

 the above and all other possible sources of error, we should 

 doubtless discover our inference to be correct. 



We usually find very little disease before the procreative 

 period which is not due to mal-E. For instance, the mortality 

 in a properly regulated boys' school is very small, and this in 

 spite of the fact that many of the boys have had their health 

 injured by an improper bringing-up in the nursery. 



It is very seldom, in fact, that we find children carried off 

 by disease due to an inherited morbid taint. Indeed, if we 

 eliminate the deaths due to the specific contagia, and to the 

 neglect of the simplest sanitary laws, such as those pertaining 

 to food, exercise, air, and clothing, we shall find that children 



