352 IMMUNITY AND CURATIVE INOCULATIONS 



and multiplies within it, or if poison-producing microbes 

 lodge somewhere beneath the skin in a wound, and keep 

 on discharging virulent poison into the blood ! The 

 mischief is spread all over the body at once. 



It is not surprising, then, that the long course of 

 natural selection and survival of the fittest has resulted 

 in the fixing in the blood and the living cells immediately 

 connected with it of extraordinary protective powers. The 

 floating scavenger cells (eater-cells or phagocytes, first 

 recognised as such and so named by Metchnikoff) are 

 already found in the blood of quite simple animals in 

 worms, shell-fish and insects. I have watched them with 

 the microscope at work in transparent minute living 

 water-fleas eating up and digesting microbes which had 

 got into the water-flea's blood. In higher animals what we 

 call " inflammation " is a condition the result of a new 

 and advantageous mechanism which consists in a local 

 retarding of the blood-current, effected by the action of the 

 nerves on the muscular walls of the blood-vessels, and the 

 consequent escape of the eater-cells into the injured or 

 infected tissue, there to eat up and destroy the injurious 

 microbes or other particles. Special and remarkable pro- 

 perties chemical activities of an extraordinary character 

 have been gradually developed in the floating phago- 

 cytes, and in similar non-floating fixed cells over which 

 the blood flows. 



These special chemical activities are of several distinct 

 kinds. The first is the power to convert the poison of a 

 microbe into a destroyer of that poison toxin into anti- 

 toxin. The atoms of these poisons are elaborately 

 composed combinations of the organic elements. By a 

 " shake " or a " twist " (so to speak) administered by the 

 living cells of the blood the combination is altered, and 

 the toxin becomes an antitoxin, destroying by chemically 

 combining with it the very toxin from which it was 



