BY DR. BURDON-SANDERSON. 247 



coating of soft sealing-wax, for which purpose it is necessary 

 to warm them in the flame of a lamp. In doing this, care must 

 be taken not to heat the point, c. A battery and Du Bois's 

 induction apparatus and key. The key must be interposed in 

 the secondary circuit. 



A frog having been curarized just sufficiently to paralyze its 

 voluntary muscles, a straight line is drawn from the notch 

 along the upper surface of the board in a direction parallel to 

 its edges. Two small perforations are made in this line, a 

 couple of millimetres from each other, at a distance from the 

 notch equal to that from the web of the frog to its occiput. 

 Through these perforations the needles are thrust, so as to pro- 

 ject about 5 millimetres, after which the board is arranged in 

 such a way on the microscope, that the V-shaped notch rests 

 over the stage aperture, and the opposite end on a support at 

 the same level. All being now ready, the integument is opened 

 along the middle line of the back of the neck, and the occipital 

 bone perforated in the middle line with a fine awl, close to its 

 posterior margin. The frog is then laid, back downwards on 

 the board, in such a position that one of the needles enters the 

 cranium through the hole in the occipital bone, the other the 

 spinal canal. The web is then laid on a plate of glass which 

 covers the notch, and secured if necessary by fine pins. Finally, 

 the heart is exposed as before. 



On opening the key for a moment, so as to allow the induced 

 current to pass through the needles, it is seen that all the arte- 

 ries of the web at once contract, the contraction increasing for 

 four or five seconds and then gradually subsiding. If the ex- 

 citation is continued for several seconds, the circulation stops. 

 To judge of the effect accurate^, it is desirable, first, to fix 

 upon an artery for observation beforehand, and bring it well 

 into view ; and secondly, to measure its diameter before, during, 

 and after excitation. For this purpose, a sheet of paper is 

 placed on a board in such a position that its surface is at right 

 angles to the direction in which the image is thrown by the 

 prism (see fig. 219), and at a distance of about 10 inches from 

 it. The outlines of the vessel are then traced on the paper with 

 a fine hard pencil. During and after excitation, other tracings 

 are made in the same way; by comparison of which the changes 

 of the diameter of the vessel can be accurately estimated. The 

 microscope must of course be so placed that light is received 

 from the side, and that the surface of the paper is sufficiently 

 illuminated to enable the observer to distinguish the point of 

 the pencil. To insure success in this fundamental experiment, 

 the following precautions must be attended to. The dose of 

 curare must be very small, and should therefore be given an 

 hour or two before the observation is made. One at least of 

 the electrodes must be inserted within the cranium ; for if both 



