182 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 42. 



subjects for investigation may be mentioned lakes situated at great 

 altitudes, isolated oceanic islands, unexplored and not yet colonized 

 regions (man is probably one of the most active factors in this dis- 

 persion), and brackish waters of vaiying degrees of salinity. 



The value of limnologic and hydrobiologic research in its relation 

 to fish culture and hygiene is now universally admitted, quite apart 

 from its theoretical interest, and every student of fresh-water biology 

 knows that rotifers are frequently the predominant group, and 

 always an important one, furnishing one of the most valuable char- 

 acteristics. As an example may be cited Lauterborn's recent work 

 on the fauna of the Rliine,^ according to which a list of the rotifers 

 from a certain body of water enables the specialist to decide whether 

 it is pure and rumiing, stagnant and full of vegetation, or polluted 

 and putrid. But the determination of rotifers can not usually 

 be made with certainty except from living or carefully prepared 

 specimens, conditions demanding not only time and equipment 

 usually not available on expeditions or limnologic campaigns, but 

 an experience which few have the time to acquire. 



As the methods suitable for Crustacea and Planarians are useless 

 here, I have, in order to overcome these difficulties, tried to discover, 

 and I believe have found, a method which, without being as simple 

 as placing the whole catch in alcohol, will allow any careful worker 

 and especially a resident naturalist to prepare rotifers in bulk in 

 such condition that they may be useful for subsequent study. The 

 method now used exclusively for the preparation of rotifers as objects 

 for the microscope is due to Rousselet;^ it consists in. narcotizing 

 the animals with a cocaine solution, followed by fixation with osmic 

 acid and mounting in weak formalin solution. I have succeeded in 

 reducing its application to animals in large quantities to an almost 

 automatic process. 



The necessary reagents are : 



1. A concentrated narcotizing solution (about three times as strong 

 as Rousselet's original formula) : 



Cocaine hydroclilorate gram.. 1 



Pure methyl alcohol cubic centimeter.. 10 



Distilled water do do 10 



Instead of cocaine one may use the same amount of stovaine, or 

 /?-eucaine hydrochlorate. 



2. A solution of osmic acid of 1 per cent strength, to which is 

 added 1 per cent chloro-platinic acid, commonly known as platinic 

 chlorid, sold either in the form of crystals or as a 10 per cent solu- 

 tion. The latter is added to prevent reduction of the osmic acid, 

 which in this way mil keep almost indefinitely. 



1 Arb. aus dem kais. Gesundheitsamte, Berlin, vol. 22, 1905, pp. 630-652. 



» Joum. Quekett Micr. Club, ser. 2, vol. 6, 1895, pp. 5-13; also Proc. 4th Int. Congr. Zool., Cambridge* 

 1898 (published 1899), p. 197. 



