416 



SCIENCE 



[N. S. Vol. XXXIV. No. 874 



of the value of fc. This appears from the fol- 

 lowing : 



Trom equation (1) we have 



I ^ = logio ^'o + 



(, 



10 



• logio Qu 



whence 



Iogioi-o+('^''-loSioeio) 



, 10 -='"'"■ ^ i» /. (4) 



Of course in order to use the simpler equation 

 (2) one must calculate out the values of the 

 constants and these vary, it must be remem- 

 bered, with the nature of reaction involved. 



And now for an example or two to illustrate 

 the application of these formulae. Barcroft 

 and King" studied the effect of temperature 

 upon the dissociation of hemoglobin. In one 

 series of observations an aqueous solution of 

 pure crystals under 10 mm. Hg pressure 

 showed at 14° C. 92 per cent, saturation; at 

 38°, 24 per cent, saturation. What is the 

 temperature coefficient for intervals of 10 

 degrees ? 



This is answered by using either equations 

 (1) or (3). Substituting the observed values 

 in equation (1) we have 



whence Q^„ = 1.75, the temperature coefficient 

 for intervals of 10 degrees. 



From equation (2) or (4) we can now calcu- 

 late the values of k for the whole of this series 

 of Barcroft and King's observations. 



By comparing equations (1) and (3) it will 

 be seen that Q^, = 10^'>\ Since Q,, = 1.75, 

 i = .0243 and therefore a in equation (2) 

 equals — .3579. For the special case under 

 consideration, then, equation (2) reads 



logio fc = — .3579 + .0243 t. 

 The table of observed and calculated values of 

 h stands as follows : 



Calculated, 

 Per Cent. 

 96 

 54 

 38 

 27 

 Journal of Physiology, 



Another and very different example may be 

 taken from the physiology of nerve. As is 

 well known, frog nerve at a temperature of 

 20° C. conducts the impulse at a rate of about 

 30 meters per second. It has, furthermore, 

 been shown that the temperature coeiEcient, 

 or the value of Q„ in the above equations, for 

 the conduction time of frog nerve,' is about 2.3. 



Now if the nature of nerve in both frog and 

 man be essentially the same, the value of Q^^^ 

 is also the same, and from equation (4), which 

 is another expression of (1), we may proceed 

 to calculate the velocity of the nervous im- 

 pulse in man. 



The known values are substituted in (4), 

 taking 37° as the body temperature of man, 

 whence 



/37-20 , „ \ 



A: =10'°°'"*°+VT5-''°-'»=-V 



or fc^ = 123.6. 



The same result is obtained from equation 

 (2). For since ()„ = 10i<'-6, then £ = .0362, 

 and for the special case of frog a = 0.753, 

 because 



log„ 30 = a -1- .0362 X 20. 



For the special case of man, then, 

 log„ i; = 0.753 + .0362 X 37, 



whence h = 123.6. 



From the above, therefore, we deduce that 

 the velocity of the nervous impulse in man is 

 about 123.6 meters per second. Can this be 

 corroborated by experiment? Happily it can. 

 Professor Piper,' of Berlin, has been able to 

 measure the conduction time of the median 

 nerve in man by using the very sensitive and 

 promptly reacting thread galvanometer. From 

 his results he calculates a rate from 117 to 125 

 meters per second. Using a similar gal- 

 vanometer, I have been able to confirm this in 

 our laboratory 



Charles D. Snyder 



The Johns Hopkins University 



° Snyder, C. D., ArcMv fiir Anatomie und Physi- 

 ologie. Physiologische Abteilung, 1907, S. 117; 

 American Journal of Physiology, 1908, Vol. 22, 

 p. 309. 



' Piper, H., Arehiv fiir die gesammte Physiol- 

 ogic, 1908, 124, p. 591. 



