1984 Journal of Applied Microscopy 



fluid, in which the specimen is left for an hour or so if picro-acetic is used, but 

 only 5 to 10 minutes in aceto-sublimate. The washing-out in case picro-acetic 

 or aceto-sublimate is used is invariably done with 50 or 70 per cent, alcohol to 

 which after aceto-sublimate a few drops of alcoholic solution of iodine are added 

 to complete the extraction of sublimate. 



The best stains for entire mounts are borax carmine, alum carmine, and alum 

 cochineal. Ha^matoxylin is liable to give an overstain which is difficult to 

 extract. Both haemalum and Czokor's alum cochineal are excellent for staining 

 Hydras it is intended to section. 



The aceto-sublimate consists of a saturated aqueous solution of corrosive 

 sublimate, to which five per cent, by volume of glacial acetic is added. The 

 picro-acetic contains one part of glacial acetic to ten or more parts of saturated 

 aqueous solution of picric acid. Exact proportions do not seem to be important, 

 but it is well to remember the swelling action of acetic acid on all tissues and 

 avoid an excess. Slight swelling of specimens to be mounted whole is rather an 

 advantage, inasmuch as it renders them more translucent and the cellular struc- 

 ture more easily seen. It should be avoided for specimens that are to be 

 sectioned. For the latter I have found aceto-sublimate a better fixative than picro- 

 acetic. Herbert P. Johnson. 

 West Roxbury, Mass. 



Vegetable and Animal Cells. 



Most workers in biological science, especially young teachers, realize how 

 difficult it is to provide simple yet comprehensive material from which the stu- 

 dent may get his first conception of the structure of the vegetable and animal cells. 

 The lesson is one of great importance, as all will agree, since it involves the mor- 

 phological unit of animal and vegetable structure. 



In this lesson, following closely the one on the use of the microscope, besides 

 learning the integral parts of the cell, the student should learn something of self- 

 reliance in manipulation, especially that which pertains to simple fixing, selective 

 staining, washing and clearing. For this reason, mounted slides should be kept 

 in the cabinet and only brought out to supplement what the student will so inter- 

 estingly have discovered for himself. 



The onion, or onion bulb, is always easily secured, and from it may be 

 obtained the material for the study of the vegetable cell. The onion should be 

 cut into halves and a piece given to each student. He is then directed to 

 separate the layers with a pair of forceps. Clinging to each scale is a delicate 

 vegetable membrane. This is carefully lifted off with the forceps and with 

 shears is snipped into pieces as large as the end of a lead pencil. These pieces 

 are immersed for three minutes in 30 per cent, alcohol. This is toyf.v them. 



While the above pieces are fixing, a single fresh piece may be mounted in 

 water. This will show in faint outline the nuclei and cell walls, giving the stu- 

 dent an idea how the specimens appear unstained. 



The student is now ready for staining. Two of the above fixed specimens 



