observed between the dogs, yet they are as nothing when compared with the enormous variation of function between the dog and the human being. The bones and garbage swallowed without injury, and the licking of its body, show the different type of digestion and assimilation, the action of the kidneys, of the various senses, and the possession of senses which we are unable to appreciate; in short, its distinctive type of existence proves the impossibility of drawing safe inferences for man from the digestive or other canine functions. Again, observation and rational experiment, solely for the benefit of one species of animal, may incidentally lead to the benefit of other races of animals; but direct experiment on one type, for the supposed benefit of another kind, is unscientific.
It is this error that vitiates the famous postulates of Professor Koch, through the system of 'controls,' the latest exemplification of this fallacy being the attempt to prove the existence of cholera in man by cultivating the bacilli in animals. The same error also produces the failure of M. Pasteur to prevent hydrophobia in man.
It is well known how the influence of what
