D. E. GODDARD ON MANIPULATION WITH CANADA BALSAM. 129 



The water bath — especially a small one — is much more under con- 

 trol, and by carefully regulating the temperature, can even be used 

 with advantage when manipulating with chloroform and balsam. 

 From many experiments and numerous disappointments, I arrived 

 at this conclusion. The centre of the slide should never be allowed 

 to come in contact with hot metal, either on a water bath or table. 

 I, therefore, in 1863, designed a table ; the drawings and measure- 

 ments are fully explained in a paper I read before the Microscopi- 

 cal Society of London, in January, 1864, and which was published 

 in the " Journal of Microscopical Science" for that year. I have 

 used it incessantly since that time, and I have never found it fail 

 when ordinary care was taken. I have left a batch of 12 slides on 

 it for 50 hours, the lamp burning underneath, and have never 

 found the balsam boil. It is impossible to boil the balsam unless 

 a very large flame is urged for a long time. I once imagined 

 that slides required long continued heat, in order to harden the 

 balsam sufficiently to be cleaned off. That opinion has been very 

 much modified ; my plan now is to submit them to a moderate 

 heat for some 15 or 20 minutes, and then suddenly to remove them 

 to a cold plate of metal of about ^th of an inch in thickness, where 

 they are allowed to cool. This, repeated several times, will gener- 

 ally be sufficient, and a very convenient method of getting rid of 

 any air bubble without the risk of spoiling the preparation by pres- 

 sure, the sudden contraction of the balsam answering the require- 

 ments. 



Another fruitful source of annoyance is the appearance of a 

 white cloudiness, which spoils many carefully mounted specimens. 

 This may arise from two sources. 



Dampness of the specimen, or the presence of grease or fatty 

 matter that has not been carefully removed before applying the 

 balsam. 



If a section of any sponge, such as may often be found on our 

 sea coast, be mounted months after it has been gathered, this 

 cloudiness will ensue, because it has not been thoroughly dried. 

 To avoid such mishaps, I employ one of three methods. 



1. — Heat, sometimes direct, but more generally by means of a 

 water bath. 



2. — By digesting the structure in strong alcohol before placing 

 it in camphine. 



3. — By using a sulphuric acid bath, which consists of a large 



