16 



Journal of Applied Microscopy. 



the closed end as evaporation proceeds 

 and to ultimately climb up onto the 

 gelatine surface to escape the evils of 

 drying. 



POSITIVE HYDROTROPISM. 



If now the Plasmodium is about to 

 fruit, it will be seen to quit the gelatine 

 surface and seek the dryer parts of the 

 filter paper or perhaps flow out onto the 

 exposed and dry surfaces of the slide be- 

 fore rounding itself into sporangia (ne- 

 g-ative hydrotrophy). On a large scale 

 hydrotrophy may be demonstrated by 

 placing large pieces of wood containing 

 Plasmodia in battery jars with a few 

 inches of water in them and covering 

 the jars with a window pane or other 

 close fitting glass cover. Wlien ready 

 to fruit the Plasmodium will squeeze it- 

 self through 'between the edge of the 

 jar and glass plate and form sporan- 

 gia on the outer surface of plate and jar. 

 At times so strong is the reaction that 

 strands of protoplasm may be seen to 

 erect themselves in the air several mil- 

 limeters in search of the source of wa- 

 ter vapor. 



Hydrotropism, if not a form of chem- 

 otropism, is certainly closely related to 

 it, and the motile forms of the myce- 

 tozoa lend themselves to the most varied 

 experiments in the latter field. By the 

 addition of any chemical substance to 

 the moistened filter paper upon which a 

 Plasmodium is resting in such a culture 

 box, as described above, the positive or 

 negative reaction may readily be ob- 

 served in the advance or retreat of the 

 migrating protoplasm. Solutions of tar, 

 sugar, salt, extracts of decaying wood 

 and leaves, glycerine and any of the 

 laboratory reagents may 'be tried with 

 success. 



In the experiments with minute Plas- 

 modia and myxamoebae, capillary glass 

 tubes, partially filled with reagent to be 

 tested, may be mounted under the cov- 

 er glass along with the organisms. The 

 air space which is left in the tube 

 should be at the closed end. If it is de- 

 sired to study the reaction of the larger 

 Plasmodia under high powers, it will be 

 necessary to substitute a coat of gela- 

 tine in the moist chamber for the more 

 easily prepared strip of filter paper. 

 Though a number of slides may be 

 quickly coated with gelatine and stored 

 away in a slide box for future use, all 

 that is necessary to get them ready for 

 use is, to soak them in water before 

 transferring the Plasmodia to them. The 

 transparent layer of gelatine will not de- 

 tract from the value of the preparation 

 for high power work. 



The chamber described above may be 

 used as a drying chamber and a gas 

 cham'ber by cementing a piece of small 



glass tubing into suitable openings made 

 in opposite corners of the box, and con- 

 necting one tuibe by means of rubber 

 tubing with a dry air or gas supply, 

 while the other tube is left for the exit 

 of the reagent. In this way and by the 

 use of the filter paper and gelatine sub- 

 strata, experiments in the immuniza- 

 tion of the Plasmodia against any toxic 

 substance may he readily conducted. 



Much remains to be done in the field 

 of electrotro'phy in its broadest sense, 

 and the careful study of the action of 

 the induction current on protoplasm, e. 

 g., a Plasmodium, will surely lead to a 

 much better knowledge of the relation 

 of protoplasmic structure to electrical 

 energy. The gradual yet complete dis- 

 integration of particles of protoplasm in 

 the immediate vicinity of other particles 

 which survive, offers an exceptional op- 

 portunity for new discoveries in the 

 nature of vital organization. 



Mechanical stimuli are readily applied 

 to Plasmodia and the reactions are direct 

 and not in any way interfere with, and 

 the results of shaking, tearing, cutting, 

 crushing, mixing with various solid and 

 liquid bodies are easily effected either 

 upon the slide or in a test tube. 



THE PREPARATION OF MICROSCOPIC MOUNTS 



OF PLASMODIA AND MYXAMOEBAE. 



KILLING REAGENTS. 



Whole Plasmodia of any of our com- 

 mon mycetozoa make extremely inter- 

 esting and valuable microscopic prepa- 

 rations illustrative of the forms assumed 

 by naked protoplasmic bodies and of the 

 structure of protoplasm, which field is 

 still almost untouched. Besides, there is 

 the very important line of investigation 

 dealing with the chemico-physical con- 

 stitution of protoplasm, which may be 

 studied by means of micro-chemical 

 tests made on the myxamoebae and 

 young Plasmodia, as well as the mature 

 and fruiting Plasmodia. 



Plasmodia which have been transferred 

 to slides and thus been freed from sand 

 grains and other impurities which might 

 interfere with microtomic manipulations, 

 are fixed in any desired way. Any of the 

 usual fixing and killing reagents will 

 furnish good material, but, of course, 

 here, as elsewhere, the selection of the 

 reagent will depend upon the result de- 

 sired. The following reagents give the 

 best satisfaction, in the order named: 



KILLINCi REAGENTS. 



Merkel's Fluid. 

 Osmic Acid Vapor. 

 Formalin, 10 per cent. 

 Hot Formalin, 5 per cent. 

 Picro-Sulphuric Acid. 

 Picio-Formalin. 

 Formal-Acetic. 



