130 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
(2) Preparing- Objects. 
Investigation of Ova.* — Mr. M. D. Hill preserved certain quantities 
of ova, immediately after fertilisation, in a mixture of corrosive sublimate 
and acetic acid, at intervals of about five minutes, until the first cleavage 
plane made its appearance. This usually took place about 1J hours 
after fertilisation, but the time varied greatly with the temperature of 
the surroundings. After being hardened in alcohol, the eggs were em- 
bedded in paraffin, cut into sections, and stained with Heidenhain’s 
iron-htematoxylin. 
Investigation of the Attractive Sphere.f — In his study of the at- 
tractive sphere of the interstitial tissue of the liver and gonad of 
Paludina vivipara , Dr. C. De Bruyne made exclusive use of Hertinann’s 
fluid for fixing purposes. The longer the period of fixation, the better 
the results. Safranin was used as a colouring reagent. 
Investigation of the Presence of Iron Compounds in Animal and 
Vegetable Cells.;}; — Dr. A. B. Maccallum describes at some length his 
methods of study. In his first communication on the method of demon- 
strating micro-chemically the occurrence of “ masked ” iron, the reagent, 
whose use he described, was called in a general way ammonium sulphide. 
This is a term properly applicable only to the compound represented by 
the formula (NH 4 ) 2 S, but is sometimes given to solutions which contain 
either ammonium hydrogen sulphide (NH 4 SH), or to polysulphides of 
ammonium, or to mixtures of the (NH 4 ) 2 S and (NH 4 SH). Further 
experiment has led the author to the conclusion that (NH 4 SH) is more 
active than the di-ammonium salt, and that none of the polysulphides of 
ammonium have any action whatever on iron in its “masked” form. 
Information is given as to the best way of preparing the reagent, which 
should not bo kept in stock. The tissues which were teased out for 
treatment were always hardened in alcohol wholly free from iron in 
solution. To facilitate the teasing out, Dr. Maccallum frequently used 
sections made with a clean steel knife covered with absolute alcohol. 
The conclusion is come to that ammonium hydrogen sulphide may be 
regarded as a reagent of very great value in the investigation of masked 
compounds of iron, and it must constitute the final test for this purpose 
whenever the accuracy of other reagents is called in question. To get 
the best results with the use of acid alcohols, the tissues must be well 
hardened. If the tissues are fresh, or imperfectly hardened, the appli- 
cation of acid alcohols for the time sets free the organic iron, but the 
structure of cellular elements is more or less changed by the acids. 
This change will not be found to occur when the tissues have been care- 
fully hardened. Strong alcohol of 90 to 95 per cent, was found to bo 
the best hardening reagent. It can, by redistillation, be made free from 
iron, and when it is of absolute strength it neither extracts any of the 
iron compounds (hsematins excepted) from tissues, nor allows these to 
diffuse. The objections to all other hardening reagents than alcohol are 
pointed out. 
* Quart. Journ. Micr. Sci., xxxviii. (1895) pp. 316 and 7. 
t Bull. Acad. Befire, Ixv. (1895) p. 242. 
X Quart. Journ. Micr. Sci., xxxviii. (1895) pp. 179-205. 
