48 DARWINISM AND RACE PROGRESS. 



received in the hands of Metschnikoff a curious 

 and very interesting explanation. He has shown 

 that an army of small cells, called phagocytes, 

 which wander through the blood and tissues, are able 

 to attack the microbes of disease, and that after a 

 struggle they are able in many cases to kill these 

 voracious invaders. In so doing, however, the weaker 

 phagocytes succumb to the struggle, while those 

 which are left alive within the body of the convales- 

 cent patient possess the power of resisting and de- 

 stroying the particular microbe which had undertaken 

 the invasion. These resisting phagocytes, selected 

 from the rest, together with their descendants, who 

 share their resisting qualities, are able to prevent fresh 

 inroads of the same enemy. We need not, therefore, 

 assume that this acquired immunity, the sole relic of 

 the attack, indicates any change in the ordinary 

 muscle or brain cells of the body, or that the repro- 

 ductive cells are in any way altered, for the immunity 

 is due only to a change in the phagocytic army. 



The germ cells in almost every case get off scot- 

 free, and there is nothing in the organisation of a 

 child to indicate whether or not his father or mother 

 suffered from measles, or scarlet fever. It might at 

 first sight be urged, in opposition to this fact, that, 

 although we cannot recognise the child of a man who 

 suffered from measles or scarlet fever by any visible 

 sign, yet the child is in some way different, inasmuch 



