STUDY OF FRESH AND LIGHTLY FIXED CELLS. 325 



mended in the important paper of M. HEIDENHAIN, " Uber Kern 

 und Protoplasma," in Festschr. z. 50 jdhr. Jubil. d. H. Prof. 

 Geheimr. v. Kolliker (also in separate reprint), Engelmann, 

 Leipzig, 1892, p. 111. This organ offers for study, besides 

 the large epithelium-cells of the intestinal crypts, numberless 

 examples of leucocytes, an extremely favorable object. 



Larvae may be bred from adults kept in confinement, and 

 supplied with a vessel of water, in which they will place the 

 larvae of their own accord. In May gravid females may be 

 killed and the larvae extracted. The larvae must be kept in 

 frequently changed water and fed every day or two. Aquatic 

 worms may be used for feeding them, e. g. Tubifex rivulorum. 



It is extremely important that they should be fed regularly 

 and abundantly, for, if not, cell-divisions in the tissues become 

 rare, and may even cease altogether. 



Other classical subjects of study will be found mentioned 

 in the following paragraphs. 



634. Stains for Living Cells. It is sometimes of the very 

 greatest importance to be able to stain a cell in the living 

 state, even though it be but feebly and imperfectly. Methylen 

 blue, dahlia, or gentian violet may be used in solution in pure 

 water, or in an indifferent liquid ; the addition of a trace of 

 chloral hydrate will enable you to obtain a clear solution of 

 the last two in saline media. It is sometimes advisable to 

 rub them up with serum, as recommended by v. LA VALETTE 

 ST. GEOEGE. These methods are most important for the study 

 of the Nebenkern. 



The student will remember that no known reagent will 

 stain any part of the nucleus whilst alive. The " Nebenkern" 

 stains sometimes, but feebly. Most frequently the colour is 

 only taken up by certain granules of the cytoplasm, which 

 may or may not be identical with the " granules" or "bio- 

 blasts" of ALTMANN. 



These matters have already been discussed in the paragraph 

 headed " Staining ' intra vitam,' " 93. 



635. Study of Fresh and Lightly fixed Cells. -It has been 

 rightly pointed out by Flemming that so-called " indifferent" 

 liquids must not be believed to be without action on nuclei. 

 Iodised serum, salt-solution, serum, aqueous humour, lymph, 

 better deserve the name of weak hardening agents. Between 



