308 CYTOLOGICAL METHODS. 



Remove the testes ; if it is large take a fragment by a pair of 

 forceps and quickly smear along the length of a dry slide several 

 times, so as to cover as much of the middle part of the slide as 

 possible. If the cells are likely to stick, fix immediately by pouring 

 on some Flemming, Bouin, or Petrunkewitsch. Set aside for a few 

 minutes, wash off in water, upgrade from 30 per cent, alcohol, and 

 leave overnight in 90 per cent, alcohol. Bring back to water, 

 stain in iron haematoxylin, thionin, or gentian violet, etc. See 

 also Groodrich's iodine-Bouin method (under "Protozoa"). Note 

 that smears may be fixed in steam, acetic, osmic, formalin vapour, 

 or " Lucidol " ( 107, 783), or stained and fixed simultaneously in 

 Leishmann, acetic Bismarck brown ( 277), aceto-carmine ( 221), 

 or such mixtures. Smears of very liquid testes, like those of 

 Lepidoptera, are liable to be washed away if fixative is added too 

 soon. It is probably best to kill the cells in some toxic vapour, 

 then allow them to dry a little, and then fix in a liquid. 



FOOT and STROBELL (Arch. f. Zellf., Bd. xii, 1914) recommend the 

 following : Place testes in drop of acidulated (acetic) " water " on end 

 of slide, and with fine needle (No. IX.) cut from it the area at stage 

 required (previously ascertained by examination oi sections). Push 

 this area by point of needle to middle of slide and break up the tissue by 

 gently tapping with the needle (never roughly spread as recommended 

 by some workers). This should be done under dissecting microscope. 



See also Kernschwarz, and ' ' Iron Carmine," 222. For BATAILLON and 

 KOEHLER'S borax-methylen-blue see Gomptes Rendm, cxvii, 1893, p. 521. 



664. The So-called Microchemieal "Tests" for Chromatin.* 



Among these the " digestion tests " have met with some favour. 

 It is well-known that examination of the partly digested tissue from 

 the gut of animals which eat fresh cells (e.g. parasitic hymenoptera) 

 shows that the nucleus of the cell resists digestion for the longest 

 time. On the other hand, there are a whole series of enzymes which 

 are specially concerned in the hydrolysis of nucleic acid, each acting 

 on some particular substrate ; these enzymes are grouped together 

 as " nucleases." The results of tests carried out with proteolytic 

 enzymes on the nature of unidentified cell granules must not be 

 depended upon too much. Extracts of such organs as the spleen 

 and pancreas are known to contain more than one kind of enzyme, 



* By " chromatin " I mean that material which forms the substance 

 of the chromosomes. The question of chromatin, nucleoli, and basophil 

 granules is one of the most difficult in Cytology. (See GATENBY, Quart. 

 Jour. Micr. Sci., vol. 64, 1920, Science Progress, January, 1921, 

 E. LUDFORD, Jour. Boy. Micr. Soc., 1921, and recent numbers of the 

 Quarterly Journal of Microscopical Science.) 



