this head. With the numerous and minute hygienic enactments of the great Jewish lawgiver for the guidance of the people of Israel we are all familiar. Prompted, we may suppose, in part by the example of Moses, and also by considerations growing out of the nature of the climate in which he lived, Mohammed incorporated with the mingled reveries, ethics, and blasphemies, which composed his Koran, dietetic rules and observances of regimen that are to this day implicitly obeyed by his zealous followers."[71] If circumcision is not a factor in the difference that exists between the Jewish race and other races, if it goes for nothing as an exemptor of disease and the promoter of longevity, then there must exist some other factor or cause that induces these conditions. What this factor is, the legislator, the sociologist, and the physician should make it their business to find out. CHAPTER XV. PREDISPOSITION TO AND EXEMPTION AND IMMUNITY FROM DISEASE. The peculiar differences that exist between different animals in regard to their susceptibility to the action of drugs is even more remarkable than the differences that exist in their susceptibility to certain forms of disease. We can understand and appreciate what Koch tells us in regard to the different susceptibilities exhibited by the house-mice and the field-mice to the anthrax bacillus, or why a nursing child should offer different results, when exposed to the diphtheria bacillus or the contagious poison of any of the exanthemata, from those witnessed in the meat or promiscuously dieted child. We can also appreciate that different individuals have different susceptibilities to disease, as well as we understand that the same degree is not always in an unvarying point of resistance or susceptibility in the same individual. The investigation and study of these conditions teach us, however, that there is a cause, or that there are causes that induce and modify this susceptibility. But there are conditions that are as yet beyond our comprehension. Take, for instance, two animals, both vertebrates, mammals, and dwelling together, eating the same food, and even having a mutual understanding or sympathy of mind and affections, having a like circulation, a like brain and nervous system, it would naturally be supposed that these two would exhibit a like susceptibility to the actions of narcotic poisons; but when we are told that one dog has taken 21 grains of atropia with impunity we are staggered. Atropia may not affect rabbits (as it does not), but the rabbit does not approach man in the same close relationship as the dog. Richardson administered to a healthy young cat 7 drachms of Battley's solution of opium, then 10 grains of morphia, and a little later 20 grains more of morphia without rendering the cat unconscious. The same experimenter gave to a pigeon 21, 30, and 40, then 50 grains of powdered opium on succeeding days with no bad effect. S. Weir Mitchell gave to three pigeons, respectively, 272