PROTOZOA 141 



once by the oil immersion lens. Only ordinary daylight is required for this method 

 but it does not serve in the study of the motility of organisms. 



By special apparatus it is possible after obtaining a certain amount of skill to 

 dissect many forms of protozoa. In this way knowledge is obtained of the physical 

 properties of various portions of their bodies and it is also possible to inject various 

 chemicals into their substance. This method of study is made possible by the me- 

 chanical devices utilized by Barber to whose work the reader is referred.* 



In order to make stained preparations the material may be either smeared in a 

 thin film upon clean slides or sectioned after appropriate treatment. In each case 

 the material requires fixation. For the preparation of stained smears the Giemsa 

 method is widely used. This is briefly as follows: 



1. Make thin smears of material on a clean and dry slide. 



2. Fix immediately by covering the smear with pure methyl alcohol which should 

 be allowed to act for ten to twenty minutes. 



3. Dry by waving slide to and fro. 



4. Stain for four to twenty-four hours, according to the depth of stain desired, 

 in a solution made by an addition of one drop of Giemsa stain to i c.c. of distilled 

 water. 



5. Rinse with distilled water. 



6. Dry and mount in immersion oil or any acid-free balsam. 



It is frequently desirable to keep stained smears unmounted as they apparently 

 retain their color for a longer period of time. They may be studied with the oil 

 immersion lens but the oil should at once be rinsed off with xylol, for if left upon the 

 preparation an insoluble substance is formed which produces a clouded appearance. 

 All stained preparations should be stored away from the light when not in use. For 

 the above method it is important to have all glassware perfectly clean and without 

 trace of acid. The stain must_ be used immediately after preparation. Certain 

 materials may be smeared very readily with the platinum loop ordinarily used in 

 bacteriology. A very practical method for making blood smears is to gather a 

 minute drop of freshly drawn blood from a small needle-prick of the skin on one 

 edge of the end of a slide. The latter is placed in contact with the surface of another 

 slide and being held at an angle of 45 degrees is pushed steadily lengthwise across its 

 surface. By increasing or decreasing this angle a thicker or thinner film may be 

 made. Certain investigators prefer to use what is termed the wet method for the 

 fixation of smears. In this case the smear is dropped face down immediately and 

 before drying into a fixative composed of two parts of a solution of saturated HgCU 

 in distilled water and one part of absolute alcohol. The technic -employed in the 

 staining of sections is then followed and the smear is not allowed to dry at any step 

 in the procedure. 



The preparation of stained sections requires a considerable amount of technical 

 skill. Tissue is first fixed to render its structure permanent. It is then dehydrated 

 in alcohol of increasing strengths, next placed in chloroform or some other clearing 

 reagent and it is then imbedded in paraffin, after which it may be sectioned. For 



*Barber: University of Kansas, Science Bulletin 1907-4-3; also Journal of Infectious 

 Diseases, 1911, 8, 248, an4 1911, 9, 117, 



