58 



Mr. C. E. Walker. 



[Jan. 9, 



cells in malignant growths apparently go on dividing mitotically for a number 

 of generations with the reduced number of chromosomes.* 



Note. — January 8, 1906. — The following fixatives have been used and in every case the 

 results described have been found with all the fixatives. Fleniming's Fluid (strong 

 formula), Hermann's Fluid, Acetic Acid and Absolute Alcohol, Corrosive Sublimate and 

 Acetic Acid, and strong Formic Acid. As it is possible that these observations may 

 interest some who are not conversant with cytological methods, it is perhaps permissible 

 to point out that the greatest care must be taken with the processes of fixation, dehydra- 

 tion, imbedding, staining, etc. Extremely small pieces of tissue should be placed in the 

 fixative within about a minute of the death of the animal or removal from the living 

 body. The dehydration should be carried out in short stages, an increase of 10 per cent, 

 of alcohol at a time being perhaps best. This does not of course apply to the tissues 

 fixed in Acetic and Alcohol or strong Formic Acid (40 per cent.), from which the tissues 

 are transferred immediately to absolute alcohol. At the same time it is necessary that 

 the tissues should not be left in under 80 per cent, of alcohol for more than two or 

 three hours after fixation. In imbedding, no higher temperature than 45° Centigrade 

 should be used. These remarks apply particularly to mammalian tissues, but also to all 

 animal tissues. Throughout the process of staining and mounting the greatest care must 

 be taken that the sections do not become even partially dried upon the slides. 



It is almost necessary to use a 10-inch tube microscope with a monochromatic light. I 

 have used apochromatic objectives' and eye-pieces specially constructed for the long tube 

 by Zeiss. With a monochromatic light it is possible to obtain excellent definition with a 

 27 or even 40 compensated ocular and a 2 or 3 mm. apochromatic objective. Anything 

 approaching this is impossible with the ordinary short tube. 



In view of the enormous advantage gained by using a monochromatic light, the stains 

 must be chosen with regard to the colour of the light used. The part of the spectrum 

 "between the blue and the green gives the shortest wave-lengths that can be conveniently 

 used. As this gives a better definition than the parts of the spectrum with longer wave- 

 lengths, red, yellow and orange stains give the best results. 



DESCRIPTION OF PLATES. 

 Plate 7. 



Fig. 1. — Myeloplax from bone-marrow of guinea-pig, showing nuclei apparently dividing 

 amitotically. 



Fig. 2. — Ditto, showing pluripolar spindle figure. 



Fig. 3. — Ditto, showing two nuclei with somatic spiremes. 



Plate 8, 



Fig. 4. — Ditto, showing nuclei that have divided and the cytoplasm dividing (amitosis). 

 Fig. 5. — Adjacent cells in the bone-marrow of guinea - pig, showing stages of 

 differentiation. 



Fig. 6. — Mononuclear cell from bone-marrow of guinea-pig. The somatic spireme is 

 formed. 



Figs. 7 and 8. — Later stages in the somatic type of division in similar cells. 



* Farmer, Moore and Walker, " On the Resemblances exhibited between the Cells of 

 Malignant Growths in Man and those of Normal Reproductive Tissue," ' Roy. Soc. Proc.,' 

 December, 1903. 



