EHRLICH'S HYPOTHESIS 251 



mown of a mother who had suffered from syphilis bearing infected 

 :hildren to a diseased father, though probably the union of such 

 nothers with such fathers is not very rare. Obviously, a father 

 can never confer immunity, for immunity is a reaction made by 

 phagocytes and perhaps some other cells functionally concerned, 

 not by the germ-cell, the function of which is reproduction. 



418. It is clear, then, that in syphilis there is no transmission 

 of acquirements in the Lamarckian sense that is, the child does 

 not develop under the stimulus of nutrition characters which the 

 parent developed under the stimuli of injury and use. The child 

 acquires the disease and, if it survives, immunity, as the parent did, 

 through infection with a microbe which has previously lived in 

 another person. Therefore the expression ' hereditary syphilis ' is 

 erroneous. It would be as reasonable to speak of a bullet which 

 passed through the mother and lodged in the child as a hereditary 

 bullet. 



419. An explanation of immunity at present very popular 

 amongst bacteriologists, is Ehrlich's 'side-chain' hypothesis, 

 a chemico-physiological attempt to interpret the facts. This 

 hypothesis resembles Darwin's theory of pangenesis, Weismann's 

 theory of germinal selection, Mendel's theory of segregation, and 

 many others, in that it is not founded on actual evidence. It seeks 

 to account for facts believed to be true by assuming conditions not 

 yet ascertained to exist. Ehrlich supposes that the cells of the 

 body possess side-chains composed of molecules, receptors as 

 they are termed, the primary function of which is to attach to the 

 cells various kinds of food molecules, fats, carbohydrates, oxygen 

 and the like. The receptors, therefore, are of different kinds. 

 In addition to having an affinity for this or that kind of food- 

 molecule, this or that kind of receptor may have an accidental 

 affinity for this or that kind of toxin an affinity which is a 

 positive and fatal disadvantage, for the cell is thereby rendered 

 susceptible to poison. If much toxin be present, many 

 receptors combine with its molecules and the cell perishes. If 

 little is present, some of the side-chains alone perish and are shed, 

 combined with the now inert toxin, and undergo subsequent 

 disintegration in the blood serum. This may be termed the 

 chemical part of the theory. The physiological part is the 

 supposition that the loss of side-chains stimulates the cells to 

 excessive production of them. The appropriate receptors are 

 thus set free in the blood which consequently becomes antitoxic. 

 Immunity is thus acquired. It is not stated whether this excessive 



