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THE POPULAR SCIENCE MONTHLY 



Cent., and then slowly cooled. The resist- 

 ance increased up to 90, and thenceforward 

 gradually decreased. In cooling, resistance 

 steadily increased from 200 down to the 

 room-temperature. This increase was so 

 great that at the end of the experiment the 

 resistance was six times what it was at the 

 beginning, temperatures being equal. The 

 same bar having been again heated from 

 20 to 200 Cent., there was no turning- 

 point, and the resistance decreased steadily 

 to the end, and increased continuously 

 throughout in the cooling ; but at the end 

 the resistance was less than at the begin- 

 ning. 



Bar 2 behaved essentially like bar 1 ; the 

 turning-poiut, however, was much higher, 

 viz., 140. With bar 3 five series of experi- 

 ments were made, and with quite similar re- 

 sults. With the first heating there was a 

 turning-point, which did not appear with 

 after-heatings. At the maximum temper- 

 ature, the resistance was pretty constant, 

 while the resistances at the beginning and 

 end of the experiments were very irregular. 



Destrnetion of Germs at Low Tempera- 

 tures. Prof Tyndall, in a communication to 

 the London Royal Society, shows how heat, 

 when diseontinuously applied, though the 

 temperature be below the boiling-point 

 of water, effectually sterilizes organic infu- 

 sions. In all such infusions, he observes, 

 there is a period of latency preceding their 

 clouding with visible bacteria. During this 

 period the germs are being prepared for 

 their emergence into the complete organ- 

 ism. They reach the end of this period 

 of preparation successively, the period of 

 latency of any germ depending on its con- 

 dition as regards dryness and induration. 

 The author's mode of proceeding is this : 

 Before the latent period of any of the 

 germs has been completed say a few 

 hours after the preparation of the infusion 

 he subjects it for a brief interval to a 

 temperature which may be under that of 

 boiling water. Such softened and vivified 

 germs as are on the point of passing into 

 active life are tliereby killed ; others not 

 yet softened remain intact. This process he 

 repeats well witliin the interval necessary 

 for the most advanced of those others to 

 finish their period of latency. The num- 



ber of undestroyed germs is further dimin- 

 ished by this second heating. After a 

 number of repetitions, which varies with 

 the character of the germs, the infusion, 

 however obstinate, is completely sterilized. 

 The periods of heating need not exceed 

 a fraction of a minute in duration. Sum 

 them up in the case of an infusion which 

 they have perfectly sterilized : they amount 

 altogether to, say, five minutes. Boil an- 

 other sample of the same infusion continu- 

 ously for fifteen or even sixty minutes, and 

 yet it is not sterilized, although the tem- 

 perature is higher and its time of applica- 

 tion more than tenfold that which, diseon- 

 tinuously applied, infallibly produces bar- 

 renness. 



Extiaction of a Prehistorie Race. The 



extinction of the partially civilized race who 

 once dwelt in the Rocky Mountain region 

 was probably the result of some great geo- 

 logical change. The country is naturally 

 arid, but doubtless when this nearly-for- 

 gotten people dwelt here in the numerous 

 cities whose ruins are still to be seen the 

 conditions of life were more favorable. 

 The annals of this interesting race have 

 perished with them, and the history of their 

 downfall is now matter for conjecture. Mr. 

 F. S. Dellenbaugh, of the Buffalo Society 

 of Natural Sciences, describes as follows 

 the course of events which resulted in the 

 extinction of the Shinunios : When the 

 change occurred, ' the inhabitants, not un- 

 derstanding the science of irrigation, be- 

 held their crops slowly but surely failing 

 every year. The inevitable result was fam- 

 ine. By this their hardy constitutions were 

 weakened, and the way was prepared for 

 some great epidemic that swept away thou- 

 sands, and left them in a melancholy con- 

 dition. Then the epidemic was, possibly, 

 soon followed by the appearance of the In- 

 dian, so entirely different from the Shinumo. 

 He was ferocious, treacherous, cunning. 

 Lying, cheating, stealing, murdering, were 

 his pastimes. Then, it is no wonder that 

 the Shinumo, in his emaciated condition, 

 was compelled to retreat before the impetu- 

 ous attack of such a foe. He was no war- 

 rior no hunter. He had depended almost 

 entirely on his knowledge of agriculture for 

 his peaceful existence. It was impossible 



