2596 Journal of Applied Microscopy 



ing the operation carefully with the eye almost on a level with the lower edge of 

 the objective. With all ordinary objectives, except those of high power, this will 

 bring them too close to the object. Then observing through the ocular slowly 

 raise the objective by means of the coarse adjustment until the object comes 

 into view. Then lastly with the fine adjustment bring into exact focus the 

 portion desired. Burton J- Howard. 



Bureau of Chemistry, U. S. Dept. of Agriculture. 



(To be Continued.) 



The Technique of Biological Projection and Anesthesia of 



Animals. 



COI'VKIC.HTEI). 



XIX. DIRECTIONS FOR MOUNTING LIVE ORGANISMS IN GLASS 



CELLS. — Concluded. 



C. Mounting animals in open top cells. 



The demonstration of the circulation of luatcr through colonies of spongilla. 



This experiment not only illustrates in an interesting way a life phenomenon 

 exhibited also by marine sponges, but shows the sensitiveness of the sponge 

 cells to heat and their contractility. Colonies of spongilla frequently have their 

 oscula at the ends of very delicate and nearly transparent tubular extensions of 

 the body substance beyond the spicules. These tubes may be seen with a hand 

 magnifier on examining in sunlight a submerged colony which has not been dis- 

 turbed for some time. 



To demonstrate, by projection, the outtiowing current of water and the sen- 

 sitiveness to heat of the cells composing the oscular tube, take all of a small 

 colony, or as much as possible of a larger one, and transfer it on its natural sup- 

 port, i. e., on the twig of green plant or fragment of the wood on which it has 

 grown, to an open top cell (Fig. 9, No. 14 or 17). If the transfer is made quickly 

 so that the colony does not dry off at all, the tubes will soon be found to be 

 normally expanded. Fasten the colony in place in the cell either by blocking 

 up or, in No. 14, by the use of the movable partition, spring and wedge so that 

 the tube will appear in profile extending outward from the surface of the colony 

 when projected on the screen. Use a low power objective. To make the out- 

 flowing current from the oscula most evident, place in the cell a few very small 

 pieces of decaying leaves from an aquarium, or any other small objects which 

 will neither float at the surface or quickly sink to the bottom of the cell. These 

 floating fragments are drawn slowly to the osculum, are caught and sent whirl- 

 ing around in a vortex caused by the steadily outflowing current. 



Under the heat stimulus -which the intense light carries with it, the delicate, 

 almost transparent oscular tubes are seen to contract slowly in diameter and 

 length; but they will again expand to their normal size, if the exposure to heat 

 is not too intense or long continued. 



