MUSEUM OF COMPARATIVE ZOOLOGY. 259 



Probably no single work within the past few years has furnished a greater 

 impetus to the investigation of the structure of nuclei than the extensive and 

 systematic observations published by Auerbach ('74) in 1874. To avoid the 

 possible influence of surrounding protoplasm on nuclear reactions, observations 

 were conducted on nuclei mechanically separated from the cells, as well as on 

 those left in their natural positions. Liver and othe(r cells from the carp ex- 

 hibit, besides 1-4 centrally located nucleoli, numerous exceedingly small 

 and faint granulations (Zwischen-Kornchen) evenly distributed through the 

 " Grundsubstanz," save that a clear area is left about each of the nucleoli and 

 sometimes a corresponding area just within the nuclear membrane. In Auer- 

 bach's opinion, this appearance is due to the repulsive influence of the nucleoli 

 and the nuclear membrane upon the " Zwischen-Kornchen," which are mova- 

 bly suspended in the soft matrix (Grundsubstanz). Eimer, however, has in 

 Auerbach's opinion assumed too much in maintaining that this feature is 

 general for fully active nuclei, and has reproduced appearances which only 

 arise with the use of hardening reagents. 



There is space here for only a brief statement of the action of reagents 

 which Auerbach has described at considerable length. Water employed to 

 gradually dilute the menstruum in which the nuclei are examined first causes 

 a shrinking in the nucleus, accompanied by the expression of a hyaline fluid 

 (Wasserschrumpfung), Accompanying this there may be an absorption of 

 water from the more fluid portions of the nucleus by its denser constituents 

 (innere Quellung), whereby an apparently homogeneous condition results. 

 There is not, however, an actual melting together of the constituents. A 

 more attenuated condition of the menstruum leads to a restorative swelling 

 (Wiederaufquellung), which may, especially with pure distilled water, cause the 

 nucleus to swell beyond its original proportions (Ueberaufquellung), but never 

 destroys it. 



Auerbach finds that solutions of common salt, bichromate of potash, acetic 

 acid, and probably other substances, vary much in their eff'ects upon nuclei, ac- 

 cording to the degree of concentration employed. The hardening and especially 

 the shrivelling effect is by no means always in direct proportion to the concen- 

 tration of the reagent, A shrinking of the nucleus is caused b}'- very dilute 

 conditions of the reagent (extending from about 1% to 0.01%), and while even 

 more dilute solutions (up to 0.001%) cause an "innere Quellung," it appears 

 that there is often another and quite distinct series of concentrations (extending 

 in common salt, e. g., from 1.5% to 14%) which produce essentially the same 

 result. Solutions of sugar, whether concentrated or dilute, cause nuclei to 

 swell. The shrinking influence of weak solutions of acetic acid and the swell- 

 ing effect produced by solutions of sugar may therefore be made to counter- 

 balance each other to a certain extent by a proper mixture of the two reagents, 

 whereby a comparatively indifferent fluid may be produced. The action of 

 neutral solutions of carmine is, aside from the staining, essentially like that of 

 acetic acid. 



These results, obtained by the treatment of nuclei mechanically freed from 



