432 The Anatomical Record.

A New Device for Maintaining a Uniform Temperature of a Warm Stage for Microscopic Work.

BY

GEORGE WALKER, M.D. Associate in Surgery, Johns Hopkins University.

By employing this dcvice I have found it possible to keep a warm mi- croscopic stage at a uniform temperature. The principle involved is similar to that made use of in the hot water heating apparatus of houses. The coil is made of half-inch brass piping continuous with which are two upright arms about 50 cni. in length, which are connected to a box made of thin copper sheeting and measuring 8.5 cm. square, by 2.5 cm. in thickness. I n the centre is a perforation 1.7 cm. in diameter, through which light comes upward to the specimen. On the upper sur- face are two other openings connected with the chamber, through which the apparatus can be filled with water. On the right and left lateral surfaces respectively is an opening for connection with the pipe, and on the right a second perforation for a thermometer. A bucket for holding the hot water and a tripod complete the apparatus.

The coil and box are completely filled with water, care being taken that every particle of air is expelled; otherwise the circulation of the water will not be satisfactory, nor the temperature regular. The coil is then placed in the bucket of water, which in turn rests on a tripod with a Bunsen burner under it. A thermometer is placed in the bucket and the temperature of the water raised to a point three degrees higher than that required for the box. After this has been reached, the flame is lowered and regulated SO that the temperature of the w-ater in the bucket remains practically the same. As the water in the bucket he- comes hot it flows upward through one pipe to the box. There i t is slightly cooled and thcn descends through the other pipe. This circula- tion is continuous, and thus a constant temperature of the stage is main- tained.

As each apparatus varies slightly in shape, a test wil have to be made to ascertain the difference between the temperature in the box and that in the bucket below. After this has been established, it can easil- be main- tained.

The Anatomical Record. 433

I have found that the temperature in the box can be kept without varying more than half a degree for any length of time after the flame

has been suitably adjusted. This adjustment is very easy and does not require more than two or three inspections, and a slight lowering or turn- ing up until the proper temperature is reached.