A RESUME OF THE USES OF FORMALIN. 75 



The plates are then placed in a closed vessel, in the bottom of 

 which is laid paper or cotton saturated with formalin. After 

 twenty-four hours the cultures are fixed. Test-tube cultures are 

 closed with a plug of cotton that has been wet with formalin, and 

 then placed in a closed chamber as above. After twenty-four hours 

 they are removed and sealed with sealing wax, when a permanent 

 preparation is obtained. Colonies from plate cultures may be 

 permanently mounted by the following procedure : The selected 

 colony is cut out of the plate and placed on a slide and covered, 

 and then a little of the melted medium is run under the cover. 

 The slide is then exposed to the action of the vapour of formalin 

 for twelve hours. Formalin renders ordinary culture media, gela- 

 tin, and that fluidified by bacteria, non-liquefiable by heat. The 

 above-mentioned method of preserving bacteria has been employed 

 successfully by Alleger, Cheesman, and many others. I am 

 informed by Dr. Cheesman that cultures treated in this manner by 

 him a year ago are still well preserved, but some of the chromo- 

 genic forms have lost their colour to some extent. 



Displacement of Spines. — T, Kirk shows that the effects of 

 introduced animals and plants upon the old fauna and flora of 

 New Zealand go to prove the truth of Darwin's theory of the 

 " survival of the fittest." Native plants have been unable to sur- 

 vive the changed conditions accompanying the advent of civilisa- 

 tion, and their places have been occupied by an army of encroach- 

 ing weeds. Further, the invading army of plants has brought in 

 its train a still more dangerous host of animals, those whose 

 agency is most dreaded being members of the Invertebrata : the 

 mussel scale, the black scale, and many others, together with 

 numerous species of plant-lice belonging to lowly-developed forms 

 of Insects. Higher in the scale are the Hessian fly, wire-worm, 

 turnip fly, and others, while numerous species of earthworms, 

 mollusca, birds, and even mammals, affect alike both fauna and 

 flora. More than five hundred plants have become naturalised in 

 the colony, but it seems probable that the limit of encroachment 

 is nearly reached, so far as introductions from Europe are con- 

 cerned. There are numbers of " repeats " also, for out of one 

 hundred and three species of plants recently introduced with bal- 

 last from Buenos Ayres, eighty-six were already naturalised in the 

 colony. — -Journal of Botany. 



