744 



SCIENCE 



[N. S. YoL. XLIII. No. 1117 



and substantial, which has an independent existence 

 and, -whatever it consists of, depends upon noth- 

 ing else. Whence we conclude, that any given vis 

 viva is of determinate quantity of which none can 

 disappear except it reappear in the effect pro- 

 duced. Hence it follows at once, that vis viva is 

 always preserved, and so perfectly that what in- 

 hered in one or many bodies before action is now, 

 after action, necessarily found itt another or in 

 several others excepting what remained in the 

 first system. And this we call the conservationem 

 virimn vivarum. 



Compare this with the modern statement : 

 In any system the variation of energy is equal 

 to the external work done by the system less 

 the work done by external forces upon the 

 system. 



John Bernoulli was under no misapprehen- 

 sion as to the importance of the principles he 

 had stated. He says in substance: Whether 

 bodies are regarded as communieatiug motion 

 to one another or whether one considers the 

 various modifications of the motion of one and 

 the same body depending on its own force 

 (where nothing can vanish without an equiv- 

 alent eilect), "pro fundamento et principio 

 universal! poni debet conservatio virium 

 vivarum, hoc est illius facultatis agendi." 



George F. Becker 



serpent dread in the primate family 

 Apropos of the discussion which has been 

 appearing in Science relative to fear of 

 snakes, I am impelled to observe how un- 

 familiar some writers on an evolutionary topic 

 appear to be with what Darwin, himself, the 

 fountain head of evolution, may have had to 

 say on the subject. 



Darwin, in his " Descent of Man," second 

 edition, Appleton, 1892, page 72, calls atten- 

 tion to this primal instinct in man and 

 monkeys, and gives an account of how his ex- 

 periments with monkeys in the zoological 

 gardens confirmed the previous experiments of 

 Brehm, in establishing its presence in the 

 whole primate family. 



While not agreeing with ]\Ir. Dabney in his 

 785) in 1864 defined the potential of one or more 

 forces as "leur pouvoir moteur total." B. Peirce 

 in his great work on analytical mechanics, 1865, 

 always uses "power" instead of "energy." 



conclusions that India is pointed to as the 

 place where a snake-fearing creature would 

 most likely originate because of the abundance 

 of poisonous snakes there (serpents of the 

 constrictor class would be even more of a 

 menace to those " long tailed, pointed eared 

 ancestors " of ours if Huxley's further deduc- 

 tion be accepted that " they were probably 

 arboreal in their habits"), it seems to me that 

 the evidence is overwhelming in favor of " ser- 

 pent dread " being a vestigial instinct — excep- 

 tions to its presence in persons like Mr. Mc- 

 Clellan to the contrary notwithstanding. 



In my own case, though for years a teacher 

 of zoology, and accustomed to the handling of 

 snakes, I confess to never having been able to 

 entirely overcome a certain shuddering dread 

 of them, and am convinced that my repugnance 

 is not due to early teaching on the subject. 

 I am sure that this is the normal attitude of 

 the members of the human family, and the 

 rest of the primates as well, toward snakes. 



That very young children may not have as 

 yet developed in them this fear is no argument 

 against its being an inherited instinct. 



There are many such instincts that do not 

 appear until the period in life when the exer- 

 cise of them would operate most strongly for 

 the protection of the species. 



It is a well-known fact that the young of 

 the primates are quite helpless for a relatively 

 long period, and during this stage of their 

 existence are carried 'about and cared for ex- 

 clusively by the mother. There would ordi- 

 narily be no protective service performed by 

 the exercise of " serpent dread " in the young 

 during this period. 



Nor is it a matter of much weight against 

 the instinctive character of the fear that it is 

 not always very discriminating zoologically. 

 It is enough that there is some suggestive re- 

 semblance or association in the object which 

 arouses it. 



A shadow made by an old hat shied over a 

 flock of young chickens will be just as effective 

 in sending them scurrying to cover, as that of 

 the hawk itself, and will evoke from the 

 mother hen just as surely the characteristic 

 warning cry. Also a crooked stick met with 



