44 PRACTICAL HISTOLOGY. 



lymph in, which can be easily made by heating a 

 piece of glass tube red-hot in the blowpipe-flame, 

 and then removing and drawing it out before it has 

 time to cool), and allow it to till with blood from 

 the heart, exposed as above directed. Now lay the 

 tube aside for an hour, and meanwhile the particles 

 with which the white corpuscles are to be fed may 

 be prepared. This is done in the following way : 

 A few drops of salt solution are poured into a watch- 

 glass, and a cake of Indian ink is rubbed in it until 

 when thoroughly mixed up the fluid has acquired 

 a faint grayish color. When left to itself fora time 

 the coarser particles subside, whereas the finer ones 

 remain longer suspended. At the expiration of the 

 hour the blood is taken and its contents are blown 

 out upon a glass slide, the clot which has formed 

 within the tube being removed, leaving merely the 

 exuded serum. This contains a few red blood-cor- 

 puscles and a large number of white ones, the latter 

 having by virtue of their amoeboid movements 

 migrated, during the space of time the tube has 

 been left, from the clot into the serum. With the 

 drop of serum a little of the salt solution containing 

 line suspended particles of the pigment is thoroughly 

 mixed, and the preparation is then covered, the 

 edges of the cover-glass being surrounded with oil 

 or melted paraffin, to prevent evaporation. When 

 the preparation is observed it will be seen that the 

 white corpuscles have quite their normal appearance, 

 whereas the colored ones for the most part exhibit 

 folds or plaits upon their surface, having undergone 

 a slight shrinking, owing to the increased density 

 of the fluid in which they lie. The black particles 

 from the Indian ink are scattered irregularly over 

 the fleld ; and although they may here and there 

 be in contact with the white corpuscles, it is never- 

 theless to be readily made out that the substance of 

 the latter is entirely free from pigment. But after 

 a short time, if the corpuscles are closely observed, 

 it will be seen that they are gradually faking into 



