5 6 THE POPULAR SCIENCE MONTHLY. 



are not definitely contradicted by anything that we know, but are as 

 yet still further from being fully sustained by facts ; and they all 

 prove to be beset by difficulties when they are subjected to a critical 

 analysis. Thus, " it must be admitted that we do not at present ap- 

 jjear to have the means for framing a complete and consistent theory 

 of volcanic action, but we may hopefully look forward to the time 

 when further observation and experiment shall have removed many of 

 the existing difficulties which beset the question, and when by the 

 light of such future researches untenable hypotheses shall be elimi- 

 nated and the just ones proved and established." 



Modern speculation, recognizing that the worlds of our system are 

 bound by the same laws and had the same origin, now tends to look 

 to the study of what is going on in the sun and planets as a valuable 

 aid in ascertaining the reason of the operations to which our planet is 

 and has been subjected. 



+ 



PHYSICAL EDUCATION. 



By FELIX L. OSWALD, M. D. 

 HYGIENIC PRECAUTIONS. 



"Dangers we can not avoid we must learn to defy." Lessistg. 



CREATURES in a state of nature can almost dispense with sani- 

 tary precautions ; Providence has secured their safety in that 

 respect. Animals are born with the instinct that enables them to dis- 

 tinguish wholesome from injurious plants. In the wilderness, where 

 the neighborhood of man does not tempt them to brave the winter of 

 the higher latitudes, most birds emigrate in time to avoid its rigors ; 

 those that stay can rely on their feather- coats ; natural selection has 

 adapted their utmost power of endurance to the possible extremes of 

 the atmospheric vicissitudes. The sexual instinct of wild animals is 

 limited to certain seasons and months that preclude the possibility of 

 their young being born at any but the most favorable time of the 

 year. From birth to death the children of Nature can trust them- 

 selves to the guidance of their hereditary inclinations ; all the contin- 

 gencies of their simple lives have been amply provided for. 



These provisions do not apply exclusively to a state of affairs which 

 the agency of man has in so many ways modified or even reversed ; 

 still, it would seem as if Nature had failed to make adequate allow- 

 ance for the possibility of certain perils incident to our artificial mode 

 of life. This fact is perhaps most strikingly illustrated by the treach- 

 erous non-repulsiveness of certain mineral poisons. The offensive 

 taste of poisonous plants seems to be proportioned to the degree of 

 their noxiousness ; hemlock, strychnine, and opium are forbiddingly 



