452 SUMMARY OF CURRENT RESEARCHES RELATING TO 



be obtained witli the ordinary aqueous solutions of picric acid, osmic 

 acid, &c. The disturbance of the osmotic equilibrium, on transferring 

 delicate cells from sea-water to fresh-water solutions, resulted in intra- 

 cellular derangements. Parallel trials were therefore made of picric 

 acid, osmic acid, and iodine, three different solutions of each being 

 made; one in distilled water, one in alcohol, and another in sea- 

 water. The solutions in distilled water and alcohol proved almost 

 worthless in each case, while each of the solutions in sea-water gave 

 good results. It was found, curiously enough, that the protoplasm 

 of the cells was more easily injured than the nuclei and karyokinetic 

 figures. 



Solutions of osmic acid and corrosive sublimate in sea-water gave 

 good preparations, but the iodine solution was regarded as the best 

 reagent. 



A few drops of a saturated alcoholic solution of iodine, added to 

 the sea-water, gives the desired results. The algae remain in the 

 solution ^1 minute, and are then transferred directly into 50 per 

 cent, alcohol. 



Dr. C. 0. Whitman considers this a valuable method which may 

 be of considerable imj)ortance to zoologists as well as to botanists. 



Arrangement of Diatoms.* — M. P. Barre gives the following 

 directions : — 



Canada balsam is spread by a metal or ivory blade a few milli- 

 metres in breadth on a cover-glass, so as only to leave a layer of 

 extreme thinness. The balsam w'ill become hard if the cover-glass 

 thus prepared is warmed over a spirit-lamp ; bubbles will form if the 

 heat is too great, but these are easily avoided by care during the 

 heating, and the balsam forms a hard brittle enamel, free from streaks 

 and blisters. This heating should be prolonged until the balsam 

 becomes modified in colour and slightly reddened. The cover-glass 

 is then placed on a black ground, and we proceed to the arrangement 

 of the diatoms by means of a very fine eye-lash fixed in a handle, 

 using the Microscope to pick them out and a strong magnifier to 

 arrange them on the smooth and even surface of the balsam. When 

 the diatoms are in place, we ascertain whether they are i^erfectly 

 straight, and those which are not in their proper place are lightly 

 slipped along by means of an eye-lash soaked in chloroform, in order 

 to remove all grease from it, and prevent the diatoms from sticking 

 to it. 



The cover-glass is then again slowly heated. The balsam becomes 

 again softened, and the diatoms sink into it, and, without altering 

 their arrangement, become semi-transparent, at which point the 

 heating must be stopped. 



Many lines may thus be arranged on the same cover-glass, the 

 balsam being reheated several times, in which case it is better not to 

 overheat it the first time, in order to avoid its becoming reddened by 

 repeated applications of heat. 



The cover-glass with the diatoms has now to be fixed on the slide. 



* Bull. Soc. Belg. Mkr., ix. (1883) pp. 7i-7. 



