2676 



Journal of Applied Microscopy 



--\ji.eLst 5>0r(\\\t 



blooded animal. Having counted the number of pulsations per minute while 

 the clam is in water at ordinary room temperature, cool the water in the cell to 

 45° or 50° F. by adding ice water, and again count the pulsations. Next add 

 warm water enough to raise the temperature of the clam to 90° or 100° F. and 

 note the increased rate of pulsation. 



Clams prepared in this way may be kept alive in a tank of fresh clear water 

 for some days, and used for several demonstrations by projection as well as for 

 study with the eye and hand lens. 



C. Vah'tdar action m the heart of a live animal and the movement of blood 

 through the heart : 



This is an optical demonstration of one of the most completely hidden phe- 

 nomena of the circulatory system. Nearly all the species of animals which have 

 well developed cardiac valves also have hearts and surrounding tissues so opaque 



as to prevent observation of their valves in 



I V\ I J_1A-J action during life. The nymphs of certain 



\\I \ W ^i ...> species of Dragon-fly of the genus Agrion, 



illustrated in an earlier article in this series 

 (Figs. 7 and 8, March, 1903) and described in 

 the succeeding issue (April, 1903) are best 

 adapted to this demonstration, but Daphnia 

 pulex may also be used. It is probable that 

 other animals will be found which may be used 

 in this demonstration, and notice of such dis- 

 coveries will be appreciated by the writer. 



In selecting a nymph choose one with as 

 little color as possible in the terminal segments 

 of the abdomen, as seen under a hand mag- 

 nifier or dissecting microscope. To anes- 

 thetize the nymph place it in one per cent, 

 chloretone solution in a watch-glass. Fill a cell of suitable size and shape 

 (Fig. 9, Nos. 5, 6. or 7), with the same solution and place the specimen in it 

 with its dorsal side up, and cover with a selected glass. Place the specimen 

 on a compound microscope and, using a one-half or three-fourths inch 

 objective, focus into the last segment but one of the animal's abdomen. 

 Adjust the mirror for a strong light and use a diaphragm of small aperture. 

 The heart is thin walled, is widest near its posterior end, and narrows 

 gradually anteriorly. When seen in optical section from the dorsal side, 

 the walls and valves appear as in the diagrammatic sketch. Fig. 11. The 

 blood enters the heart at its posterior end through two valved openings, one 

 on each side near the central line of the organ. During diastole the anterior 

 and posterior sides of the open valve are parallel, but during systole they are 

 pressed closely together, and the rate of pulsation is so slow that their move- 

 ments are easily followed. One must guard against being deceived by a vigorous 

 and somewhat irregular muscular action, which moves the tracheal trunks 

 situated on each side of and close to the heart, and is, apparently, concerned 

 with the operation of the rectal tracheal gill. Streams of blood carrying many 



-I— - A>rxcV«<]L 





Fig. 11. — Diagrammatic sketch of the 

 termmal somites of the abdomen of 

 a nymph of Dragon-fly {Agrion) 

 showing the position of the heart 

 and its valves as seen in optical 

 section. 



