4 METHODS. 



tissues may, as long as they remain alive, exhibit under the 

 heatable stage changes of shape, but, on account of their being 

 imbedded in basis or cement substance, no locomotion. 



The heatable stage of S. Strieker is a shallow metal case, the 

 central cavity of which is connected with small pipes for the 

 conduction of gases to be brought in contact with the living 

 specimen. The latter rests on the lower surface of the covering- 

 glass. In front of the case a metal peg can be connected with a 

 spiral copper wire, the distal extremity of which is heated over 

 an alcohol or gas lamp. The temperature is shown by a small 

 thermometer outside the case. If a drop of blood be inclosed 

 between two thin covering-glasses, with greased edges, the 

 phenomena of amoeboid motion and locomotion are much better 

 observed than in a drop hanging on the lower surface of one 

 cover only. For high powers of the microscope, a condenser of 

 light must be put into the diaphragm of the stage, as a good deal 

 of light is lost on account of the unavoidable depth of the stage. 



Electricity. Living specimens are sometimes exposed to the 

 influence of the electric current, preferably the induced, inter- 

 rupted, as that alone admits of proper action upon the specimen. 

 Both the constant and an induced current extending over several 

 minutes are objectionable, as electrolysis with formation of gas- 

 bubbles occurs, and the thermic action may destroy the effects 

 of electricity upon the specimen. The simplest apparatus for 

 applying electricity under the microscope is that of E. Brucke. 

 A glass slide is covered with strips of tin-foil, between which, in 

 the center of the slide, rests the specimen. The lower surface 

 of the glass slide, also covered with tin-foil, is moved on two 

 parallel copper supports attached to a larger glass plate, and in 

 connection with the electrodes. 



Preparation of Fresh Tissues. Tissues from the freshly killed 

 animal are, as a rule, unfit for microscopic research beyond a 

 limited time. There is no liquid which keeps the specimen un- 

 changed, and, without the addition of some liquid, the specimen 

 soon dries. As preserving fluids have been used the liquid of the 

 anterior chamber of the eye, serum of blood, the amniotic liquid 

 of calf or sheep embryos, with the addition of a little metallic 

 iodine, normal urine, one-half per cent, solution of chloride of so- 

 dium, very dilute solution of bichromate of potassa, etc. The two 

 latter answer all purposes. Water is objectionable, as the bio- 

 plasson matter swells and becomes destroyed by it ; the same 

 destructive action is noticeable on the addition of glycerine. 



