1 882.] in the Zoological Station in Naples. 703 



tological purposes ; besides, the removal of the osmic acid leaves 

 the animal in a good condition for staining. 



Dr. Mayer's experience with Sapphirina appears to support him 

 in the following conclusions in regard to the nature of the action 

 of osmic acid, viz., that the hardening effect of the acid is due to 

 the formation of inorganic precipitates within the tissues. This 

 is made evident by the fact that the animal becomes soft and 

 flexible as soon as these precipitates are removed by bleaching. 



This method of bleaching has been used by Dr. Mayer for 

 removing natural pigment. Alcoholic preparations of the eye of 

 Mysis, for instance, can be fully bleached in toto, but with better 

 success by operating with single sections. To avoid swelling, 

 which is apt to arise by the use of aqueous fluids, staining media 

 of an alcoholic nature should be used. 



6. Chromic Acid.— Chromic solutions have in common with 

 osmic acid, the peculiarity of hardening by virtue of the chemi- 

 cal combinations which they form with cell-substances, and all 

 the consequent disadvantages with respect to staining. The use 

 of chromic acid in the Zoological Station of Naples may be said 

 to have been largely superceded by picro-sulpliuric acid, corrosive 

 sublimate and MerkeVs fluid, for it is now seldom used except in 

 combination with other fluids. 1 It is sometimes mixed with 

 'Kleinenberg's fluid, for example, when. a higher degree of hard- 

 ening is required than can be obtained by the use of the latter 



chromic acid, and to allow them to act too long. Good results 

 are in some cases obtained when the objects are treated with a 

 weak solution (> S -J< per cent) and removed soon after they are 

 completely dead. 

 /. MerkePs Fluid.— 

 Platinum ckloride&ssoUtd. in water 1:400 



Professor Merkel, 2 

 ons in equal parts 1 





