344 The Microscope. 



we bring the preparation directly into alcohol, since the eosin is 

 partially an alcohol solution. At the end of five minutes the slip is 

 taken out of the alcohol, and, in order to be quite sure that there is 

 no water still clinging to the preparation, we incline the slip at a 

 slight angle to the rag with which we are holding it, and pour a few 

 drops of alcohol from the small bottle over it. If upon dropping oil 

 of cloves on the preparation it should be dark upon a dark sleeve or 

 other dark background, we may remove the oil of cloves with a few 

 drops of xylol. Having quickly cleaned the slip close up to the 

 preparation, we place a drop of Canada balsam upon it, which must 

 be allowed to spread out before the cover- slip is lowered upon it. 



Human blood is prepared in the same way, except that here the 

 finger-tip undergoes the surgical operation. If a finger of the left 

 hand be lightly bound with a string and a sharp neeedle be held in 

 the right a quarter of an inch fi'om the end, one quick energetic 

 stroke suffices to bring a drop of blood to the surface, which should 

 be transferred to the slip by drawing it, previously moistened, across 

 the drop of blood. 



A look at our preparations with the microscope shows us that 

 the coloring substances we have used have attached themselves to 

 certain parts and certain forms of corpuscles. In the preparation 

 of the frog's blood we find that the large oval red corpuscles have 

 been colored red with eosin. The nuclei are for the most part blue 

 from hfematoxylin, the well-known coloring substance for nuclei. 

 The protoplasma, provided no coagulation has occurred, is homo- 

 geneous. The usually oval nuclei are also generally homogeneous, 

 though occasionally granulated like the nuclei of other cells. 



The white blood- corpuscles differ among themselves in form, 

 color, and the number and size of their nuclei. 1. Those coarsely 

 granulated which are deeply colored with eosin, hence their name 

 " eosinophilous cells,*' * are perhaps the most striking. Their form, 

 is usually round, and they contain from one to four nuclei. 2. A 

 second is perhaps best characterized by its large nucleus sparely 

 surrounded with protoplasma, colored blue with nigrosin. The form 

 of the cell, according to the position in which we see it, is spindle- 

 shaped, with an oval nucleus in which the granules are distinct, and 

 seem to be arranged in lines parallel to the long axis of the nucleus, 

 or it is quite round with a round nucleus. The name " hsematoblasts" 

 was given them by Hay em. 3. Another variety has, like the "eosino- 



*This name is given by Ehrlich. 



