CHAPTER XXIII. 

 MICROSCOPICAL TECHNIC. 



THE microscopic study of organisms and parts of organs is one of 

 the most important tasks of biologists and physicians. The princi- 

 pal object of the microscopist is to deduce from the form of an object 

 its nature and whether its appearance is normal or diseased. 



Remarkable progress has been made in this field though the chemi- 

 cal interpretation of the methods employed is still in its infancy. 



To prepare an object for microscopical examination it must be 

 spread out very thin upon a slide and, if necessary, made transpar- 

 ent. In the case of unicellular organisms (bacteria, protozoa, etc.) 

 no further preparation is necessary. If the presence of bacteria is 

 to be determined it suffices to spread the object in question on a 

 slide with a platinum loop and to dry it at moderate temperature 

 by drawing the slide through a Bunsen flame several times, so as to 

 coagulate the albumin. On account of the intensity with which 

 bacteria and cocci stain with basic dyes (methylene blue, carbol 

 fuschin, etc.) it is usually an easy matter to recognize them in the 

 otherwise structureless coagulum. 



Organs of higher plants and animals must be either teased or pre- 

 pared in thin sections. 



The least deceptive object is naturally the living organism, as we 

 see it, for instance, in hanging drops, in the moist chamber or the 

 microscope stage aquarium of J. Com, etc.; even in higher ani- 

 mals some investigations may be made while they are still alive by 

 spreading out portions of organs still connected with the animal so that 

 they are transparent. In this way we may see, for instance, the cir- 

 culation of the blood in the lungs and in the web of a frog's foot. Much 

 more frequently an opportunity to examine surviving tissue pre- 

 sents itself. It is by no means necessary that at the moment that 

 the animal itself dies, a given organ or cell should die. Let me recall 

 that the heart may be isolated immediately after an animal (cat, 

 frog, etc.) has been killed and may continue to beat for a long time 

 if suitable means are employed. Leucocytes of warm blooded 

 animals show protoplasmic movements, if observed at 37, even as 

 long as a half day after the animal's death. It goes without saying 

 that this must occur in a medium which causes neither swelling nor 



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