624 SUMMARY OF CURRENT RESEARCHES RELATING TO 



embryos are removed from this solution and are transferred to a 

 solution of formalin in water. After thirty to forty-five minutes the 

 embryo floated on to the water, and then transferred, by means of a 

 broad lifter, to the killing and lixing solution, consisting of a 5 p.c. 

 third dish, containing 25 p.c. alcohol ; after another two hours they 

 arc graded through an ascending series of alcohols up to 92 p.c., in 

 which they are allowed to remain. Formalin fixation is serviceable 

 when the embryos are to be mounted whole, but where sections are re- 

 quired a more precise fixative solution should be employed, such as 

 Fleming's fluid or picro-formo-acetic solution. The latter solution is 

 formed by mixing standard aqueous solution of picric acid 75 parts, 

 formalin 25 parts, and acetic acid 5 parts. After three hours the fixative 

 is washed out with 25 p.c. alcohol, and graded up to 92 p.c. alcohol. 



Staining and Mounting. — Mayer's formula for haemacalcium gives 

 specially good results, and prevents the danger of swelling which is 

 encountered with the use of hematoxylin in aqueous solution. Before 

 staining, the specimens should be placed in 70 p.c. alcohol from fifteen 

 to thirty minutes, to neutralize and prevent precipitation of the haematin. 

 For staining entire embryos, 2 oz. of the stain is added to 6 oz. of 70 p.c. 

 alcohol. The embryos are left in the stain for several hours, and, if 

 necessary, the colour may be reduced by washing out with weak hydro- 

 chloric acid. The embryos are then left in 92 p.c. alcohol for two or 

 three hours, then transferred to absolute alcohol for one hour, from which 

 they are cleared in oil of terpineol, and mounted in benzol balsam. 



For histological purposes special treatment of the embryos is necessary, 

 i.e. infiltrating the specimens with paraffin, or permeating them with 

 celloidine for sectionizing purposes. By the paraffin method the speci- 

 mens fixed with picro-formo-acetic solution are dehydrated, and trans- 

 ferred successively to absolute alcohol and chloroform (six hours), 

 chloroform (one hour), saturated solution of paraffin (130° Fahr.) in 

 chloroform (three to six hours), and then to pure paraffin in a water- 

 oven. After several changes of paraffin the specimens are moulded 

 and cooled, and sections cut in the usual way. Sections may be stained 

 with hasmacalcium. Xylol may be substituted for chloroform in the 

 clearing process, cedar-wood oil being used between the alcohols and the 

 xylol. Possibly terpineol might be used as a cheap substitute for 

 the xylol. 



The writer recommends the use of the celloidin method of embedding 

 embryos, as the tissues are less liable to be injured than by the paraffin 

 method. He only resorts to the latter method when it is impossible to 

 obtain sufficiently thin sections without the aid of celloidin. 



Collection and Preparation of Fresh-water Nematodes.* — Margaret 

 V. Cobb collected fresh-water Nematodes by taking samples of the sand 

 or mud and water of the pool or stream bottom and of the aquatic 

 vegetation. These were washed through a series of graded sieves from 

 coarse to fine which removed the coarser debris, until examination with 

 a lens showed that Nematodes also were caught on the sieve. The 

 collection was then allowed to settle for five minutes or more and the 



* Trans. Amer. Micr. Soc, xxxiv. (1915) pp. 22-3. 



