and Laboratory Methods. 1983 



temperature thermostat controlling a burner underneath. During seasons of 

 the year when the tap water is below the temperature required the water is run 

 directly into the incubator, but during the summer months, when the temperature 

 of the tap water itself is above 20° C, the water is first run through a bath of 

 shaved ice by using a coil in the ice, and then to the incubator. 



The instrument is subject to a variation of never more than three degrees, 

 which, in the designer's experience, does not materially influence the results in 

 water plate work with gelatin. At times there is considerable condensation of 

 moisture on the interior of the incubator. This can be easily overcome by using 

 a layer of coarse asbestos on which to place the plates. Coarse blotting paper 

 acts equally as well. After many attempts with other devices the one described 

 answers better than any other tried. 



The water incubator is best placed over or near a sink so that the constantly 

 running water, which at times is but a very small stream, has a free outlet. The 

 amount of water to be supplied to the incubators varies with the season of year, 

 and depends entirely on the water temperature as it enters the water jacket. 

 Dept. of Health, Buffalo, N. Y. WiLLIAM G. BiSSELL. 



A Fixation Method for Hydra. 



The common fresh water Hydras {Hydra fnsca and H. vij-idis) do not pre- 

 sent unusual difficulties to the preparateur, and yet perfect results are not always 

 obtained. The tentacles, especially, are difficult to manage. If fixed in a well- 

 extended condition, as they should be, they not infrequently become twisted 

 together, and are then extremely liable to be broken off in subsequent transfers 

 with pipette or spatula. 



The following method does away with this difficulty. It was employed by 

 the writer some years ago in the preparation of Hydra fusca in large numbers 

 for class-study, and found entirely satisfactory. Recently I have applied it to 

 Hydra viridis with equally good results. 



The Hydras are transferred from the aquarium with a pipette and placed 

 singly in watch-glasses containing just enough water to cover them. They soon 

 attach themselves and expand. Either picro-acetic or aceto-sublimate may be 

 used as a killing agent. No doubt other standard fixatives will serve as well. 

 Whatever fluid is used it must be heated nearly to boiling and applied precisely 

 as indicated. 



When the Hydra is well expanded in the shallow layer of water, its position 

 is necessarily almost horizontal. A pipette-full of the hot fixing fluid is suddenly 

 squirted into the watch-glass so that the current sweeps along the Hydra f'-om 

 its aboral to its oral extremity. It is thus instantaneously immersed in the fixing 

 fluid, in which it stiffens out and dies in an extended condition. The tentacles 

 are stretched out in a straight line coinciding with the principal axis, while their 

 tips are slightly approximated. In this position there is little danger of their 

 breaking off in reasonably careful manipulation. 



The moment the Hydra is killed the watch-glass is filled with the hot fixing 



