1899] MICROSCOPICAL JOURNAL. 347 



stratum, thus enabling- the investig^ator to examine in de- 

 tail the vertical distribution of the plankton. 



Rubber Stoppers. — Dr. H. A. Hagfan 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 w^ith rubber stoppers, two-thirds of 

 which had been in use for from ten totwelveyears,he comes 

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

 every year aftertwelve years' use,and in the first six years 

 probably only one out of two thousand. Stoppers of larg-e 

 size keep much long-er than those of small size. American 

 rubber stoppers are all made of vulcanized indiarubber, 

 and have the disadvantag-e 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 disadvantag-e, 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 disadvantag-es of the old method besides being- exceed- 

 ing-ly simple and inexpensive. An oval tin pail, of from 

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

 tig-ht 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 g-ently into the pail containing- the harden- 

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

 brain thus underg-oes hardening- in all directions at once, 



