USE OF CANADA BALSA AM. 191 



over the insects, and then one or more drops of the 

 fluid balsam are delivered from a glass rod at one of 

 the sides of these covers. The balsam runs slowly 

 under by capillarity, and it drives all the air before it, the 

 small weight of the cover assisting it to spread, until 

 the whole area is filled. No pressure is to be used, or 

 the elastic bodies of the Aphides will change shape ; 

 and besides this, the juices will be forced through the 

 cornicles and pores. If the balsam is thick, a very 

 gentle heat, hardly exceeding that of the cheek, may 

 be applied ; but, as a rule, the temperature of a room is 

 better than that which exceeds it. The insects die 

 immediately they are cut off from air, and in almost 

 every case their position will be good for examination. 

 To spread the wings of a small insect, the above- 

 mentioned small dots may be made in a row. The 

 belly of the specimen is applied to the middle spot, 

 and by a bristle one wing may be applied to the dot 

 on the one side and the other wing to the third dot. 

 The cover is then placed as before, and when the 

 balsam runs in, it will not disturb the position of the 

 spread wings. 



It will be noticed that very soon after live insects 

 have been mounted in a resinous substance that will 

 not mix with water, a white cloudiness forms around 

 each specimen. This is caused by the watery juices 

 of the insect, which "chill" the medium and make 

 it opaque. 



This cloudiness, however, entirely disappears after 

 perhaps a month, the moisture being carried slowly 

 outwards. The same is to be said of stray air-bubbles. 

 The oxygen of the air unites with the balsam and thus 

 hardens it ; but what combination is effected with the 

 nitrogen is not so clear. However, air-bubbles in 

 balsam disappear in time, provided the former is not 

 in too hard a condition. 



In cases when the above small pressure is un- 

 desirable, small circles, cut by round punches of 

 different sizes out of very thin sheet lead, will be found 



