and Laboratory Methods. 



2225 



observe the circulation of the blood and the wandering of the white blood cor- 

 puscles ; for they are easily kept alive in the laboratory, are quickly prepared for 

 study, and the arterial and venous trunks in the caudal and other tins, being 

 approximately parallel, are more apt to be found in the same field and focal plane 

 of the objective than are the corresponding parts of the web of a frog's foot. 

 Moreover, the capillaries are more easily traced from artery to vein than in the 

 frog's web. In addition, the fin-rays and their articulations and also the lateral 

 line are readily seen. 



To anesthetize goldfish for the purpose of sketching them, studying them 

 under hand lens or compound microscope, pro- 

 ceed as follows : Place the fish, one or more as 

 needed, in a tray with water enough to cover 

 them and add to the water one-twentieth its 

 volume of one per cent, chloretone solution. 

 Active swimming soon ceases, the movements of 

 the jaws, which are at first rapid, gradually de- 

 crease, the movements of the pectoral and ven- 

 tral fins become irregular and cease, and finally 

 the fish turns on its side and appears to be dead. 

 It is now in the most favorable condition for 

 sketching and for careful morphological study. 

 To prepare it for study under the compound 

 microscope place it on a piece of clear glass an 

 inch or two longer and wider than the fish, spread 

 the caudal fin, moisten the body of the fish with 

 enough of the anesthetizing solution to form a 

 little pool around it on the glass, and transfer the 

 glass plate and fish to the stage of a microscope, 

 the stage being approximately horizontal. The 

 fish does not need to be tied or pinned down. 

 If the study is to continue for a half hour or 

 more, place a piece of filter paper or cloth moist- 

 ened with the anesthetizing solution over the 

 entire body in front of the tail so as to prevent 

 the epidermis and scales from becoming dry. A 

 thin cover-glass may be laid on the caudal fin for 

 the same purpose. Focus on the caudal fin and 

 trace the blood stream from arteries through 

 arterioles, capillaries, venules and veins. Using a quarter inch, or higher power, 

 objective, examine the thin end of the caudal fin for wandering cells in the con- 

 nective-tissue between the capillaries. The leucocytes here appear flattened, 

 circular or irregular in outline, and, very granular. Examine the irregular 

 shaped ones and note the slow amceboid movements which accompany the pro- 

 jection or contraction of their pseudopodia. It is possible to make out the 

 motion of indivinual granules in the moving leucocytes. By careful focussing 

 and lighting the outlines of the epidermal cells are brought into view. 



Fig. 8.— Tracheal Gills of Nymph 

 of Dragon Fly. Photographed 

 from screen. 



