120 IMMUNITY AND INFECTION 



discrimination between nutritive substances and irritating or harmful 

 substances which may accidentally possess the same combining 

 affinity for the cell. Consequently, when poisonous substances pos- 

 sessing chemical affinities similar to those of the normal food sub- 

 stances circulate in the blood stream, they may become attached to 

 the cell in place of the normal physiological nutrients. The anchoring 

 of these poisonous substances, unlike the attachment of normal 

 nutrient substances, is followed by damage to the cell, or, in extreme 

 cases, by the death of the cell. 1 If the cell is not actually killed by the 

 presence of the toxic substance acting upon it through the side-chains, 

 it is irritated, as it were, and the toxic substance imposes a twofold 

 burden upon the cell loss of the side-chains to which it is attached 

 and which are essential to maintain the nutrition of the cell, and 

 greater or lesser damage to the function of the cell, due to toxic inhibi- 

 tion of its normal activities. A cell cannot disembarrass itself of the 

 poison, nor can it assimilate it. It can, however, throw off the side- 

 chain with the poison still firmly united to it chemically; the extruded 

 poison cannot enter into chemical combination with other cells pos- 

 sessing the same chemical affinity, for it is already attached to a side- 

 chain. Its combining power is saturated. 



Side-chains are a necessity to the cell, however; without them 

 the cell would starve. Consequently the cell regenerates new side- 

 chains of precisely the same kind to replace those thrown off after 

 being bound to non-assimilable substances. If enough of the soluble 

 poison or toxin circulates in the blood stream, this process of union 

 of toxin to the cell by its side-chains and its expulsion from the cell 

 with the side-chains attached to it is so frequently repeated that the 

 cell regenerates side-chains in excess of the normal requirements, in 

 accordance with the Weigert theory of overproduction. This casting 

 off of supernumerary -side-chains is important. Were they not cast 

 off the cell would be vulnerable to toxin in direct proportion to the 

 extra number of side-chains, which would furnish extra bonds for its 

 attachment. As the cast-off side-chains circulate in the blood stream, 

 however, they are an element of protection to the cell, for they retain 

 their original combining power for the toxin and unite with it and 

 neutralize it as it circulates in the blood stream; that is, before it 

 can reach the cell itself. It will be seen, therefore, that the same 



1 If the toxic material circulates in the blood stream but does not become attached 

 to the body cells, it is harmless to the host, according to this theory, and the host is 

 naturally immune. 



