470 



Prof. Stokes on the Communication of Vibration [June 18, 



any attempt to apply the principles of physical and chemical science to 

 the case of poisons. 



The first is as to the minuteness of the fatal dose. Any explanation, 

 before it can be accepted, must show that the cause is adequate to produce 

 the effect. This is a difficulty in the path of any rational explanation. It 

 is attempted to meet it by showing, on the one hand, that the equivalency 

 of nerve-force is extremely small, by reference to its analogy with electrical 

 currents, and by other considerations, and that therefore the degree of 

 chemical change involved in its evolution is also small ; and, on the other 

 hand, the maximum of force to be obtained from an organic body is 

 through the exercise of the affinities of its individual elements. 



The second point is as to the special action of certain poisons on par- 

 ticular nervous centres, — strychnia on the cord, morphia on the brain, &c., 

 the substances being carried by the blood to all alike. It is as necessary 

 to explain why no effect is produced on those centres, or tracts which do 

 not suffer, as to explain the action on the one which does. The explana- 

 tion is sought in the fact that the difference in the functional activity of 

 the brain and cord, the need for sleep by the brain, not experienced, at any 

 rate in the same degree, by the cord, point to a difference of tension, and 

 therefore of relation with the substances which act as poisons. This con- 

 sideration will apply where the differences of susceptibility and of tension 

 are not so marked. 



But this is only part of a still wider question — the different action of 

 poisons on different classes of animals. The explanation is still the same. 

 Difference in the functional energy or activity of corresponding nerve- 

 centres implies difference of tension. 



The following facts bear strikingly on this point : — 



1 . Ansesthetics affect all classes of animals alike, i, e. when the effect 

 is a general arrest of oxidation. 



2. Strychnia, which acts on the cord, affects all animals alike. The 

 spinal system is the centre which is most similar in its endowments in all 

 classes of vertebrates. 



3. The poisons which have the most diverse action on different animals 

 are such as in man act on the cerebral ganglia. 



XIV. ^' On the Communication of Vibration from a Vibrating Body 

 to a surrounding Gas.'' By G. G. Stokes, M.A., Sec. U.S., Fel- 

 low of Pembroke College, and Lucasian Professor of Mathematics 

 in the University of Cambridge. Received June 18, 1868. 



(Abstract.) 



In the first volume of the Transactions of the Cambridge Philosophical 

 Society will be found a paper by the late Professor John Leslie, describing 



