1899] MICROSCOPICAL JOURNAL. 34T 



stratum, thus enabling- the investigator to examine in de- 

 tail the vertical distribution of the plankton. 



Rubber Stoppers. — Dr. H. A. Hagan has made careful 

 records for the purpose of determining the durability of 

 the rubber stoppers which are used in vials containing mi- 

 croscopic objects in alcohol. From an examination of some 

 seven thousand vials with rubber stoppers, two-thirds of 

 which had been in use for from ten to twelveyears,he comes 

 to the conclusion that less than one in a thousand gives out 

 every year after twelve years' use, and in the first six years 

 probably only one out of two thousand. Stoppers of large 

 size keep much longer than those of small size. American 

 rubber stoppers are all made of vulcanized indiarubber, 

 and have the disadvantage of forming small crystals of 

 sulphur about the stopper, which becomes loosened and at- 

 tach themselves to the specimens. It is supposed that pure 

 rubber stoppers used for chemical purposes would not pre- 

 sent this disadvantage, which may be obviated, however, 

 or very much reduced, if the stoppers are washed or soak- 

 ed in hot water for an hour or two before being - used. 



Hardening. — The usual processes that are adopted for 

 the hardening of brain and similarly soft tissues,frequent- 

 ly result in failure by reason of the pressure of the tissues 

 on the hard surface of the containing vessel, and the con- 

 sequent mis-shapening of the lobes and convolutions, or 

 the rupturing of the delicate superficial membranes. To 

 prevent this, Prof. W. C. Krauss, of Nebraska University, 

 has devised a hardening- receptacle which obviates most of 

 the disadvantages of the old method besides being exceed- 

 ingly simple and inexpensive. An oval tin pail, of from 

 four to six quarts capacity, with an ordinary handle and a 

 tight fitting cover, has a series of ten hooks soldered on the 

 inside about one inch from the top of the rim. The convex 

 surface of the fresh brain is covered with a sheet of cot- 

 ton, and over this is placed a piece of netting. The whole 

 is then lowered gently into the pail containing the harden- 

 ing fluid, and suspended in it by means of the hooks. The 

 brain thus undergoes hardening in all directions at once, 



