But we must not jump to conclusions. Because we can immunize successfully against one disease, it does not follow that the same methods will immunize against another disease. Each disease is a problem in itself and may require its own methods. Nor because we can immunize the guinea-pig in the laboratory, does it follow that the same methods are applicable in the human patient. The only proof that we can immunize against hay fever is to immunize against hay fever. So, to the subject! =Passive Immunity.= The first man to attempt to apply the methods of modern immunity to hay fever was Dunbar, of Hamburg, in 1903, with this _pollantin_. He attempted to duplicate in hay fever the triumph of antitoxin in diphtheria by injecting a horse with increasing doses of pollen until the horse became immune to large doses of pollen and his blood full of antibodies. Dunbar expected to confer passive immunity on the hay fever patient by transferring to him this horse serum with its antibodies. There is no better example of the rule that each disease requires its own methods of immunity. While diphtheria antitoxin is harmless to the diphtheria patient, the serum of the pollen-immunized horse nearly killed the first patient Dunbar tried it on, who happened to be his assistant, a sufferer from hay fever. It is probable that pollantin is based on the wrong principle, that hay fever is not, like diphtheria, a poisoning by a toxin to be antidoted by an antitoxin. However, to Dunbar belongs the credit of first attempting to put the treatment of hay fever on a scientific basis and he introduced the method of testing the patient that has been followed by all later workers, dropping the pollen extract in the eye. In the _Centralblatt für Bakteriologie, Referate_, xxxvi, s. 453, there is an account of a most unseemly quarrel between Dunbar and Weichardt, the latter claiming that before leaving Hamburg, he suggested the idea of pollantin to Dunbar. Weichardt has since put on the market another hay fever specific, called _graminol_, which is the blood-serum of cattle that have fed on the offending grasses during the hay fever season. The theory is that the blood of the cow contains antibodies to those grasses and that passive immunity can be conferred on the hay fever patient by transferring those antibodies to his blood.