Journal of Applied Microscopy. 



193 



broken and very evenly mixed with salt 

 if the best results are to be obtained. 



If more rapid or practically instanta- 

 neous freezing is desired, the material is 

 placed in a suitable receiver and sub- 

 jected to the action of escaping liquid 

 carbon dioxide, a process which will give 

 much lower temperatures than any of the 

 above methods. With the cheapening of 

 liquified air it also may be utilized as an 

 agent in such methods, and protracted 

 exposures to low temperatures would 

 then be possible. 



Long exposure of material to fairly low 

 temperatures may be obtained in the 

 rooms of a cold storage establishment 

 where convenient space can be rented at 

 a low rate for indefinite periods. 



H. B. HUMI-HREY. 



Physiological Laboratory, University of 

 Minnesota. 



Cultivation of Algae in Aquaria. 



Some points relative to the cultivation 

 of Algae in aquaria may be helpful to 

 amateur workers in this line. It is the 

 usual practice to collect Algae like 

 Vaucheria, Spirogyra, etc., and put them 

 in a large glass vessel from one-half to 

 two-thirds filled with water, in the hope 

 that they will grow and fruit and thus 

 furnish a supply of material for future 

 use. Very often, however, the plants 

 soon turn yellow, decay, and rise to the 

 surface, where they form a foul-smelling 

 scum. Usually the next step is to empty 

 the aquarium. This should not be done, 

 however, as after a time the material 

 settles to the bottom, new growth starts; 

 and if any spores of the desired Algae are 

 present they will grow along with others 

 and no further trouble will be experi- 

 enced. But it is better not to risk the 

 loss of material by allowing it to go 

 through the fermentation process. In 

 order to avoid fermentation the water 

 must be kept thoroughly supplied with 

 oxygen. This can sometimes be done by 

 placing the Algae in a broad vessel with 

 shallow water, and occasionally aerating 

 by dipping up some of the water and 

 pouring it back, allowing it to strike the 

 hand held just above the surface of the 

 water in the vessel, so as to break the 

 force of the descending stream, and In 

 this way prevent the disturbance of the 

 colonies of Algae and the stirring up of 

 sediment. 



A bette^; way, however, is to grow in 

 the water some good aerating plants, like 

 Myriophyllum, Cabomba, Ranunculus, 

 water mosses, etc. — in fact any sub- 

 merg-ed aquatic plants which give off 

 bubbles of air (largely oxygen) when 

 exposed to light. Algae introduced in 

 small quantities into aquaria thus sup- 



plied with oxygenating plants will thrive 

 for long periods quite as well, if not 

 better than in their original habitat. It 

 is also well to introduce if possible some 

 little fresh-water Crustaceans; Cypris or 

 Cypridopsis are especially good. They 

 are the most harmless of scavengers, 

 living mainly on decaying vegetable 

 tissue, especially the soft tissue, or 

 parenchyma. They are particularly fond 

 of the mesophyll of leaves, which they 

 remove, leaving beautiful leaf skeletons. 

 Albert F. Woods. 



Division of Vegetable Physiology and 

 Pathology, U. S. Department of Agri- 

 culture. 



A Thermostat for High or Varying 

 Gas Pressure. 



To those who use natural gas as fuel in 

 their laboratories, the following easily 

 constructed thermostat may be of inter- 

 est. With the high pressure and the 

 great variation of the ordinary service, 

 the usual mercury regulators cannot be 

 used without the intervention of some 

 more or less expensive reducer. The 

 apparatus is described, not as presenting 

 anything new in principle, but as some- 

 thing which anyone with a little skill can 

 construct and which will perfectly con- 

 trol any pressure of gas and maintain 

 the temperature of the oven, bath, or in- 

 cubator with a variation of less than one 

 degree. 



Ohm Well 



A glass tube or bulb with a slender 

 neck is placed in a well of the oven and 

 filled with mercury, M. A wire, Wi, 

 from one pole of a battery, B, is blown 

 into its side so as to make contact with 

 the mercury. Through a cork, C, in the 

 top of the tube another wire. Wo, is 

 passed into the narrow neck and may be 

 raised or lowered at will. This wire 

 passes to the binding post of the regula- 

 tor, through the coils of the electro-mag- 

 net and to the other pole of the battery. 



The regulator consists of a small, care- 

 fully fitted wooden box fastened with 

 glue and screws. The cut represents it 



