How Science Helps the Body 167 



already at their destructive work, that they 

 become an easier prey for the ever vigilant 

 phagocytes (Fig. 15). The bodies of the killed 



FIG. 15. PHAGOCYTES AND VACCINES 



This cut shows two phagocytes from animals infected 

 with staphylococcus pyogenes the common pus-forming 

 bacterium. The animal from which the cell at the left was 

 taken was untreated. The animal from which the right hand 

 cell was taken had been treated with " vaccine" consisting of 

 a culture of these organisms killed by heat. Many more 

 bacteria have been taken up by the phagocyte of the vac- 

 cine treated animal. 



bacteria thus used are called vaccines and the 

 substances produced by the body cells under 

 their influence are known as opsonins. This 

 name is derived from a Latin word which means 

 "I prepare food for." The manufacture of 



