8 ILLINOIS BIOLOGICAL MONOGRAPHS [218 



the former, while the parasites remain motile longer in the latter. A 

 minimum amount of water or salt solution is used and a cover slip placed 

 over the material to prevent rapid evaporation. The animals are now 

 in an unnatural medium and will disintegrate rather rapidly, so sketches 

 of those which are to be measured must be made with the camera lucida 

 as soon as possible, using a minimum amount of light and a power of 

 the miscroscope of about 100 diameters. When the parasites are nearly 

 transparent, as are those of the species inhabiting the Coccinellidae, e. g., 

 a drop of iodine-iodide solution will turn them brown and thus render 

 them visible; a weak saffranin solution serves to bring out in vivo the 

 nucleus and sometimes the longitudinal striations. 



Although the parasites are best studied alive, some stained prepara- 

 tions are valuable. In order to preserve parasites in toto for future 

 study, the intestine of the host is slit lengthwise and teased apart gently 

 to loosen the food masses and the parasites. It is then dropped into the 

 fixing solution and agitated gently when the free parasites will drop to 

 the bottom of the dish. The best fixing agent is corrosive-sublimate solu- 

 tion to which has been added a trace of acetic acid; the precipitate is 

 first washed with 50% alcohol and iodine, then with 70% and iodine, 

 and the parasites preserved in 70% alcohol until needed. Picro-formol 

 after Bouin was used in some instances with good results. 



For staining in toto, two methods are advisable. The slide may be 

 smeared with a very small amount of egg albumen, the animals dropped 

 upon it from a capillary pipette and the preparation placed horizontally 

 in a dish of 35% alcohol for about two minutes to coagulate the albu- 

 men. It may then be carried very gradually down the alcohols to a 

 water solution of Ehrlich's hematoxylin or to a rather weak alcoholic so- 

 lution of borax-carmine and in the latter instance counter-stained with 

 picric acid. The alcohols and stains should be placed in flat dishes so 

 that the slide may be kept horizontal and gradualy immersed and with- 

 drawn from each solution to insure against loss of the parasites. Many 

 grades of alcohol should be used and the parasites kept in each alcohol 

 about fifteen minutes. 



If the material is abundant, the parasites may be stained en masse 

 in a small dish, since they settle to the bottom, but there is always con- 

 siderable loss in the transfer of liquids. 



When material is very scarce and all of the parasites must be kept, 

 it is best to preserve simply in glycerine. Parasites from one host intes- 

 tine can be placed on several slides. A weak mixture is made of glycer- 

 ine and water and a very little of this used, the parasites being under ob- 

 servation under the microscope the while, for it is very easy to add too 

 much glycerine and in an instant destroy all the material. The water is 

 very gradually withdrawn by adding a little glycerine for several sue- 



