HARDWICKE'S SC lENCE-GOS SIP. 



8d 



edges of the covers, particularly when soft balsam 

 has been used : it not only prevents the slipping of 

 the cover, but also the penetration of the asphalt, 

 or coloured varnish generally used for " ringing." 

 The space between the edge of the cover and slide 

 should be filled up with the mixture, and when dry, 

 the asphalt or varnish can be put on without risk of 

 running in. — F. K. 



Remounting Objects. — Most of the old injected 

 preparations were mounted in Goodby's fluid. My 

 own injections have most of them been remounted, 

 either in glycerine and water, or distilled water with 

 a drop or two of carbolic acid added (about four 

 drops of the strongest solution of the acid to 1 oz. 

 of water).— i^'.r. 



A Pkoblem in Mounting.— In preparing objects 

 for the microscope, I have occasionally met with 

 the following difficulty. A specimen, such as a 

 small insect or diatom, after haviug been duly per- 

 meated with turpentine or benzole, and all traces of 

 air thus expelled, is mounted in the usual manner 

 in Canada balsam, and apparently successfully ; 

 but when again examined, perhaps in an hour, 

 perhaps in a day afterwards, one is astonished to 

 find that an aggravating so-called air-bubble has 

 made its appearance in the interior of the specimen. 

 The mount, therefore, is worthless, for if heat is 

 applied in the vain hope of expelling the bubble 

 the blemish is only augmented. I purposely use 

 the expression astonished, for, after the air has once 

 been driven out, and the object satisfactorily 

 mounted in balsam, it is evidently impossible that 

 air can re-enter it. Whence, then, comes the 

 bubble ? This is the problem, and here is my 

 explanation. The turpentine, or benzole, has 

 entered and filled the specimen through a very 

 minute orifice or fissure, but when it is immersed in 

 the balsam, a much denser medium, that cannot do 

 so, whilst the thinner medium within the object, 

 having a natural affinity with the balsam, flows out 

 from the object to mix with it,— a process of exos- 

 mose without the corresponding endosmose. But 

 if the whole of the turpentine leaves the object, a 

 vacuum would be the result, which cannot for a 

 moment be supposed ; and so I fancy that a portion 

 of it, in the form of vapour, is left behind, and that 

 the obnoxious bubble is composed of vapour, and 

 not of air. I may be wrong, but I fancy I am 

 right in my solution of the difficulty ; for, occa- 

 sionally, having mounted an object, and placed it 

 immediately under the microscope, I have suddenly 

 seen a little black speck appear, which, as I have 

 watched it, gradually assumed the form of a con- 

 stantly-increasing bubble. In such a case as this, 

 it is generally useless to dismount the object, and, 

 after having again soaked it in turpentine, repeat 

 the process, as the same disappointment will pro- 

 bably recur. But the remedy is easy, and this is 



the useful and practical part of my communication. 

 Having dismounted the specimen, if a diatom, it is 

 only necessary to place a fresh drop of turpentine 

 or benzole on it, and, having thus again expelled 

 the bubble, to add to this with the point of a pin 

 the minutest portion of fluid balsam, which thus 

 greatly diluted will enter the object, and remain in 

 it when immersed in the denser mass. For larger 

 objects, such as insects, which must be resoaked in 

 a watch-glass of turpentine, or other kind of bath, 

 a larger portion of balsam is requisite ; the prin- 

 ciple, however, is the same, that the soaking 

 medium should be only just sufficiently densified 

 to insure the result. — Fred. H. Laing, Lower Red- 

 lands. 



ZOOLOGY. 



The American Potato-bug. — Agriculturists 

 will be relieved by the letter from the Privy Council 

 respecting the potato-bug. The accounts which 

 have reached us from the United States of the 

 ravages of Doryphora decemlineata were alarming 

 in the extreme. It seems to have been generated 

 in Iowa in 1S61. Where it once gets a footing it 

 soon makes its mark; it speedily destroys the potato 

 crop. It is believed to effect all its transformations 

 in fifty days, so that a single pair would, if unmo- 

 lested, produce sixty millions of progeny in a single 

 season. Nobody, therefore, will be at all surprised 

 to learn that the insect is travelling east very fast, 

 and has already taken up its abode in Ohio and 

 Canada. But the accounts of its marvellous 

 fecundity do not make the little creature by any 

 means a more welcome visitor to our shores, and a 

 memorial has been sent to the Government praying 

 for a prohibition of the importation of American 

 potatoes. A reply to that memorial has just been 

 received, which is very reassuring. If the informa- 

 tion it contains may be depended upon, the farmers 

 may sow their seed and rest in peace. The Privy 

 Council for Trade states that American official 

 reports establish the fact that the larvae of this 

 destructive parasite are not deposited 171 the tubers 

 or conveyed by them, and that with the exercise of 

 an ordinary amount of care, the importation of the 

 American potato can be rendered as safe as the 

 transmission of our own. It is to be hoped that 

 this fact has been shown by observation to be un- 

 doubted. Otherwise, nothing but regret will be 

 caused by the statement that " My lords consider 

 there is no reason for interfering with the trade 

 between the two countries." 



Exceptional Reproduction of certain Tine- 

 id^.— Dr. Duncan, in his "Transformations of 

 Insects," remarks that "many naturalists have ob- 

 served that the species of Solenobia, one of theTine- 

 idse, have a most exceptional power of reproduction. 



