MEDICAL WORK WITH MICROSCOPE 



in the middle of each cell is called a nucleus, it is 

 the most active part of the cell and when the latter 

 is about to divide, as it does when growth takes 

 place, the nucleus always divides first. 



Now we may perform another operation upon 

 ourselves, rather more painful than the last one but 

 not very serious. We wish to examine some human 

 blood, so we tie a handkerchief tightly round one 

 of our fingers and with a clean needle — be sure that 

 it is clean — make a puncture in the finger tip. The 

 handkerchief bandage will prevent our feeling any 

 pain. We must put the drop of blood we have 

 obtained in the centre of a clean slide and examine 

 it under the microscope. While the blood is still 

 liquid, we shall see a number of circular discs 

 floating about, they are very small being only 1 / 3200 

 inch in diameter. The centre of each disc appears 

 darker than the rim, but this darker shade is only 

 apparent. Using a term we introduced in our 

 chapter on the lens, we may call the discs double 

 concave. Now let us watch our objects for a 

 moment and we shall notice that they begin to 

 arrange themselves in chains, they appear like a 

 number of draughtsmen placed one upon the other, 

 our drop of blood is now beginning to clot. A simple 

 experiment may be attempted at this stage; we 

 must run a drop of water on to our little blood 

 discs and watch carefully what happens. We shall 

 see that they change their shape gradually, from 

 being double concave they become flat sided, and 

 this is not all, for they continue to change till both 



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