202 The Microscope. 



in order to keep it quiet, and with pins stretch out and fasten the 

 hind foot so that the web 'will be spanned tightly over the opening. 

 Fasten the whole to the stage with clips, and examine with a low 

 power. If the web be moistened with glycerin, the study of the 

 circulation can go on for some time. A little search will show a 

 number of vessels with the blood rushing through them. Select a 

 small vessel where the blood is moving slowly, and the corpuscles 

 can be easily made out. The red cells, more numerous and larger 

 than the white, will be seen massed together in the center of the 

 vessel, whilst the white cells, moving more slowly, cling to the sides. 

 The red cells are seen to be very elastic, as they double and twist in 

 going around angles in their course. Occasionally a red cell will 

 block up a channel, causing a temporary stasis. When such a place 

 is found, opportunity is given to study the amoeboid movement of 

 the white cells. Using a rather high power, the cell will be seen to 

 send out and withdraw little processes, and, even though the blood 

 current i& stopped, to move along the vessel. 



Amceboid Movements. — If the student does not succeed in 

 finding a suitable spot in the frog's web for the study of this 

 amceboid movement, he will have no difficulty in doing so in a drop 

 of blood placed on a warm slide. The slide should be kept warm 

 and moist. A warm stage can be made as follows: Take a strip of 

 copper the size of a glass slide, and make a diaphragm opening in 

 the center. Attach a long strip of copper to this— or the whole can 

 be of one piece — sufficient to reach a distance away from the stage 

 of the microscope. The flame of an alcohol lamp heating the end 

 of this strip will, by conduction, heat the whole piece, together with 

 the slide placed on it. A drop of blood being prepared for exam- 

 ination in the usual way, ma,ke a ring around the cover-glass with 

 oil to prevent evaporation, place on the warm stage, apply the heat, 

 and the leucocytes can be studied in their movements with higher 

 powers and with greater ease than was the case in the frog's web. 



Blood Crystals. — Though a number of different crystals can 

 be obtained from the blood, only one will be described here. Hsemin 

 or Teichmann's crystals are small, rhombic plates of a brownish or 

 brownish-red color. They are important, as the chemical reaction 

 necessary to produce them is simple, and their presence is a valuable 

 test for blood. They are made as fojlows: A drop of blood is dried 

 and pulverized. To a small quantity of this blood placed on a slide, add 

 treble the amount of sodium chloride. Mix intimately and apply a 

 cover-glass with a hair interposed to keep it somewhat away from 

 the slide. Now add two or three drops of glacial acetic acid, and 



