Brook : Summary of Methods of Microscopical PtESEARCH. 165 



tissues are req^iiired to be hardened more than the latter would do it 

 alone. 



Dr, Lang's Medium,. — Dr. Lang was induced by an old paper of 

 Blanchard's to work with corrosive sublimate, to which he added 

 acetic acid or picrosulphuric acid. The original prescription is as 

 folio vys : — 



100 parts distilled water. 

 6-10 „ common salt. 

 5-8 acetic acid. 



3-12 corrosive sublimate, 

 and ultimately \ part alum. 



The Planarians, for which this medium was intended, are laid oil 

 their backs and freed as much as possible from water, and the mixture 

 is then poured over them. They then die fully extemled. In half- 

 an-hour they are placed in alcohol of 70 %, then in 90 %, and finally 

 in 100 % alcohol, and in two days they are quite hardened. Later Dr. 

 Lang has used a saturated solution of corrosive sublimate in picro- 

 sulphuric acid with 5 % acetic acid added ; or simply a saturated 

 solution of corrosive sublimate in water. In cases where it is difficult 

 to kill the object suBiciently quickly, the liquid must be used boiling. 

 According to the researches of Lang and others, this medium is very 

 useful for liydroids. corals, small Cumopliores, some Gephyrea and 

 Balanoglossiis^ Echinoderms, Sagitta, many annelids, and for Rhobdo- 

 coda. Dendrocoela should only be preserved by this method when 

 wanted for histological purposes. To the foregoing may be added 

 C^sfoda, Trematoda, and larvse of Turhellaria. As a rule Planarians 

 killed by this method should not remain more than a few days in 

 alcohol, as they become very brittle. It is better to stain them at 

 once and imbed in paraffine ready for section cutting, where they may 

 remain for a considerable time. Wi'h the Arthropoda Dr. Mayer has 

 not been able to obtain good results by this method. 



Prof. MetlceVs Medium. — This consists of a solution of one part each 

 of platinum chloride, and chromic acid in 800 parts of water. Dr. 

 Eisig has obtained very good results by this method with annelids, 

 and thinks that as a rule four to six hours is a sufficient time for the 

 objects to remain in the medium. After further treatment with 

 alcohol, the objects stain splendidly. 



(To he continued.) 



