52 PRACTICAL HISTOLOGY. 



One or more amoeboid white corpuscles which happen 

 to be in the path which the spark must take in 

 traversing the interval between the points are kept 

 in view, and the spark is then allowed to pass. The 

 white corpuscles immediately cease moving, with- 

 draw their processes, and become rounded in shape; 

 in fact, undergo general contraction. But if only 

 one slight shock be given they soon recover and 

 resume their movements, although these are often 

 somewhat altered in character. The red corpuscles 

 are but slightly if at all affected ; but if a succession 

 of shocks be transmitted from an electric machine 

 or an induction-coil, electrolytic action is set up in 

 the fluid, bubbles of gas are developed, the effects 

 respectively of acids and alkalies are set up in the 

 neighborhood of the tin-foil points, and the red 

 corpuscles undergo changes brought about by these. 



Preparation 19. Presence of Glycogen. 

 Many of the white corpuscles contain a certain 

 amount of glycogen, or animal starch, either in dis- 

 tinct granules or in a more diffused form. This 

 substance becomes stained of a reddish mahogany 

 color by solution of iodine, and may thus be readily 

 detected, both here and elsewhere. The solution to 

 be used is made by dissolving 1 gramme of iodine 

 dn 100 cc. of water, which contains 2 grammes of 

 iodide of potassium in solution. 



The preparation, preferably of frog's or newt's 

 blood, is made in the usual way, and the iodine 

 solution added at the side of the cover-glass. The 

 red corpuscles are stained of an intense yellow, but 

 are otherwise little altered, except that the nucleus, 

 which remains unstained, becomes globular, and 

 bulges out at either surface of the corpuscle. The 

 white corpuscles are instantly arrested in their 

 movements and killed, preserving exactly the form 

 which they exhibited when reached by the iodine 

 solution. Being of less specific gravity than the 

 latter, they tend to float on it ; and, if the layer of 

 fluid is thick, must be sought by focussing upwards 



