1887.] MICROSCOPICAL JOURNAL. 131 
the caterpillar, take hold of one of the loops of the silk-gland, draw it out en- 
tire, drop it in vinegar to take off its external coat, then stretch it to double or 
treble its original length and dry it. A durable filament is thus formed strong 
as cat-gut, and much cheaper. The tenacity of the filament is constantly re- 
stored by soaking it for a few minutes in warm rice water ; that is, in the water 
in which rice has been boiled for food. The fishermen say that when thus 
prepared a line will hold the largest fish taken on the coast. It was found, 
however, that a single filament would not sustain a weight of more than 44 
pounds. Dr. Caustand, in charge of the hospital at Swatow, had successfully 
used these filaments to replace ligature silk.— Proc. Acad. Nat. Scé., Philada., 
1886, p. 298. 
MICROSCOPICAL TECHNIQUE. 
An electrical constant-temperature apparatus. 
By W. C. BORDEN,.M. D., U. S. A.. 
FORT DOUGLAS, UTAH. 
In many of the details of histological technique, an apparatus for maintain- 
ing a constant temperature is a great convenience, and in some it is a neces- 
sity. 
This apparatus should be one that will not easily get out of order, and that 
can be depended upon to maintain the temperature desired. For the use of 
those who, like myself, have no gas at command, but have to use either pe- 
troleum, or alcohol, as a source of heat, the apparatus described in this article 
will be found efficient and reliable. It can be left for hours with the cer- 
tainty that, when again examined, the heat will not have gone above a cer- 
tain point, or have dropped, at any time, more than one-half, or possibly 
one, degree below it. The general form of the entire apparatus is diagramed 
in figure 2 and the regulating thermometer in figure 1. The battery used is 
the ordinary gravity battery used in telegraphy, and which can be purchased, 
copper and zinc included, for 85 cents a cell. Ihave used three cells. This 
form of battery gives a current of nearly constant quantity, and requires but 
little attention, needing to be cleaned but about once in two or three months, 
when the zincs and coppers should be taken out and scraped. The loss of 
water by evaporation should be made up from time to time, and if the clear 
solution of sulphate of zinc, which forms at the top of the jar, attains a spe- 
cific gravity of 1030°, or more, some of it should be taken out and fresh water 
added. The blue saturated solution of sulphate of copper should always 
cover the copper, and if it goes too low, add more crystals of the salt. With 
these few attentions there will be no danger of the battery breaking down, 
while in use, and so spoiling the work. The regulating ther mometer (fig. 1) 
is made by taking a small glass vial, filling the lower part with mercury, and 
the upper with 95% alcohol, corking it tightly, and passing a small glass tube 
through the cork, to the iaeorah The cork must fit very closely, and should 
be made impervious to water by soaking in melted parattine for several hours. 
The top of the tube is to be loosely corked, and two wires passed down into 
it through the cork, without touching each other—one well down into the 
mercury and the other free above it. This regulating thermometer is now 
hung in the water bath, supported by the cork Cc and When the temperature 
of the bath, as shown by a standard thermometer, has reached the highest 
point desired, the wire above the mercury (B, fig. 1) is pushed down so as 
just to touch the surface of the latter. 
