and Laboratory Methods. '-^''TT 



corpuscles may be seen surging toward the heart, entering it during diastole, 

 pausing an instant, and then rushing into the dorsal blood vessel during systole. 

 Having found the heart and its valves with the compound microscope, transfer 

 the specimen to the projection microscope and use as low a power as will give 

 the necessary magnification on the screen. The light must be very brilliant on 

 account of the partial opacity of the animal. 



Daphnia pulex may be studied in essentially the same manner as the nymph 

 of Dragon-fly. Anesthetize it in a mixture of one per cent, solution of chloretone 

 one or two parts, water five parts. Mount in a hollow-ground cell (Fig. 9, No. 3). 

 Its heart is somewhat lens-shaped with the valves on the dorsal side near the 

 lateral margins. The valves are not as distinct as in the nymph of Agrion, and 

 the normal rate of pulsation of the heart is extremely rapid. Repeated attempts 

 to count it accurately have failed, but give counts ranging from 250 to 300 per 

 minute- 

 In concluding this series of articles it is a pleasure to note that the growing 

 demand for better projection apparatus is being met by manufacturers, and that 

 the continued use of chloretone in the study of live animals is resulting in the 

 attainment of excellent, and in some cases unexpectedly delicate and interesting 

 results. It is the intention of the author to combine with this series other articles 

 of interest and value and publish the whole in the form of a complete manual of 

 biological projection. Correspondence with users of these or other methods of 

 projection and anesthesia is desired. A. H. Cole. 



5715 Monroe Ave., Chicago. 



Industrial Microscopy. 

 III. 



APPARATUS— Continued. 



The best light to use for microscopical work is that from a northern sky. 

 Direct sunlight cannot be used. The amount and character of the light enter- 

 ing the objective is a very important factor in obtaining good results. Hence 

 the value of the substage condenser and diaphragm. Colored objects or those 

 that have been artificially stained can be examined with a larger diaphragm 

 opening than nearly clear objects, such as starches, natural fibers and the like. 

 A little experimentation will soon teach the importance of this feature of manip- 

 ulation and also the most favorable conditions. 



The lenses must be kept clean. A clean old linen handkerchief or, better 

 still, Japanese lens paper obtainable from dealers in microscopes should be used. 

 Simply breathing on the lens to cover it with a dew and then gently wiping it 

 with the linen or paper will ordinarily be found sufficient to clean them. Lenses 

 should never be rubbed with the fingers. Lenses not cleaned by this method 

 should be wiped with the paper or linen dampened in alcohol, ether or xylol 

 according as may be found necessary, but excess of these liquids should be 

 avoided since part of them are solvents for the materials by which some lenses 



