ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 571 



removed by employing the forceps or cutting it round with a 

 razor. 



The entire contents having been removed the egg is freed from 

 chromic acid by leaving it in 30 per cent, alcohol for a day, the 

 alcohol being renewed until it is no longer coloured yellow. 



For staining, the egg is placed in picrocarmine for twenty-four 

 hours and washed in 30 per cent, alcohol to remove the picric acid. 

 When it has been well washed it may be kept in 30 per cent, alcohol 

 until sections are required. 



Previous to cutting sections the egg should be placed in absolute 

 alcohol for half an hour, and then for a few moments in essence of 

 bergamot. Dry and imbed in a mixture of 4 parts of spermaceti and 

 1 of cacao butter, to which is added, according to the temperature, 

 some drops of castor-oil. The knife should be moistened with olive- 

 oil and each section washed with a mixture of 4 parts of oil of turpen- 

 tine and 1 of creosote to dissolve the imbedding substance surround- 

 ing the section. Mount in Canada balsam. 



To preserve the embryo entire, the shell is to be removed as above 

 described, after coagulation. The egg is then placed in a drop of 

 water on the stage, and with a low power the embryo is extracted 

 from the vitellus. It is cleaned as much as possible, so that no 

 portion of the vitellus adheres to it, and mounted in glycerinated 

 gelatine, previously coloured with methyl-green. By this method the 

 embryo takes from the gelatine an excess of colour, and is thus stained 

 after the preparation is made. If it is coloured first and then placed 

 in colourless gelatine it will always lose colour (sometimes completely) 

 if the gelatine is only a little greater in volume than the embryo. 



Collecting, Staining, and I hotographing Bacteria.* — Dr. G. M. 



Sternberg in " a contribution to the study of the bacterial organisms 

 commonly found upon exposed mucous surfaces and in the alimentary 

 canal of healthy individuals " (which contains much interesting matter), 

 states that he has found the following to be the most satisfactory 

 method of collecting bacteria for examination with high powers and 

 for photography. 



The slightest possible smear of the material to be examined is 

 allowed to dry upon a thin glass cover, and to secure a sufficiently 

 uniform layer, it is usually best to spread it while moist with the 

 end of a glass slide. Material is obtained from the mouth by scrap- 

 ing the surface of the tongue, or of the teeth, with a clean instrument ; 

 from the female vagina by a speculum or digital examination ; and 

 from the male urethra, by applying a thin glass cover directly to the 

 moist mucous membrane at the extremity of the canal. 



A five-cent bottle of aniline violet ink furnishes an ample supply 

 of staining fluid of the best quality. Two or three drops of this 

 placed upon the thin cover will very quickly — one to three minutes — 

 give the bacterial organisms attached to its surface a deep violet 

 colour. The cover is then to be washed by a gentle stream of pure 

 water, and is ready for immediate examination, or may be mounted 



* Stud, from the Biol. Lab. Johns Hopkins Univ., ii. (1SS2) pp. 157-81 (19 

 photomicrographs). 



