ai6 THE POPULAR SCIENCE MONTHLY 



child may result from a syphilitic father and an apparently healthy 

 mother, the mother's immunity being shown by the speedy infection of 

 a healthy wet-nurse from the child's lips, while she herself nurses with 

 impunity. Conversely, Profeta's law asserts that an apparently healthy 

 child may sometimes be bom of a syphilitic mother (and father), in 

 which case it may be suckled by either the mother or a syphilitic wet- 

 nurse without danger of infection. In either case examination of the 

 blood has demonstrated the existence of the parasites as well as the 

 permanence of the Wassermann reaction, in the mother's blood in the 

 first instance, in the child's in the second. It became evident, from 

 facts of this kind, that immunity from protozoan infection (animal 

 parasites) is not the same thing as immunity from bacterial infection 

 (vegetable parasites). In the latter case the immunity is derived from 

 the antitoxic products of the bacteria themselves. In the case of the 

 animal parasites, we know nothing of the chemical sources of infection 

 and immunity. As a matter of pure speculation, perhaps the immune 

 mother in Colles's law and the immune child in Profeta's law may, like 

 the bacillus carriers of typhoid fever, come under Ehrlich's immunity of 

 the first order (natural immunity), in which the sensitive receptors 

 have either become worn out and insensitive or no longer exist as such. 

 Theorizing aside, the practical outcome of these details was the evident 

 impossibility of curing parasitic diseases by special antitoxins or vac- 

 cines, and the practical necessity of finding chemical specifics which 

 would destroy the parasites as quinine does the malarial plasmodium. 

 The next step towards a rational chemotherapy was Ehrlich's discovery 

 that when mice infected with trypanosomes are treated with specific 

 dyes like trypan red in doses that fall short of complete sterilization by 

 some assignable quantity, a race of trypanosomes can be gradually bred 

 which will prove permanently " fast," or resistant to the effects of the 

 drug. The power of parasites to immunize themselves and their descend- 

 ants against the effect of destructive poisons led Ehrlich to his next 

 move in attempting to checkmate them — the idea of sterilizing the 

 patient's body uno iciu ("mit einem Schlag") by a single dose of 

 medicine. It was " upon this hint that he spake " in formulating his 

 therapia sterilisans magna and we are now in a position to appreciate 

 the value of his discoveries in pharmacodynamics. 



In his Harben lectures before the Royal Institute of Public Health 

 in 1907 Ehrlich stated his conviction that pharmacology, toxicology and 

 therapeutics are " the most important branches of medicine." In other 

 words, he believes that the chief end of the physician is to get his 

 patients well. Self-evident as this proposition is, it has a certain para- 

 doxical novelty when we consider the dominance of setiological studies 

 (pathology and bacteriology) through the last half of the nineteenth 

 century and the apparent debacle of drug therapy which attended the 

 rise of experimental pharmacodynamics. In such natural remedies as 



