PHYSICAL DETERIORATION. 47 



dreaded scourgers in most hospitals, now occur only 

 from culpable and punishable neglect. 



The Reproductive Cells are as a Rule unaffected by them. 



A short study of these diseases should well repay 

 us, showing as it will do that in by far the greater 

 number of cases these severe constitutional derange- 

 ments produce no effect upon the reproductive cells ; 

 that they are in fact incapable of producing a change 

 that will be hereditarily transmitted. We shall learn, 

 moreover, the part that they have played, and can 

 play, in producing racial change by selection. The 

 micro-organisms of disease are of many varieties, and 

 each variety is capable of setting up its own peculiar 

 disturbance. The disturbance set up by one kind we 

 call small-pox, that arising from another kind, cholera, 

 and so on. Now, the very curious point comes out 

 that in most of these diseases, although the composi- 

 tion of the blood is profoundly altered, and many of 

 the tissues undergo marked change, this change, 

 fortunately for us, is quite of a temporary character, 

 and when the attack is over there is only one test 

 which will enable us to say that the body is not just 

 in the same condition as it was before. This test is 

 that it cannot be infected again for a long time, if at 

 all, by the same micro-organism. 



This induced immunity from further attacks has 



