78 The Microscope. 



purpose. By it, we supply the asphyxiated system with that sub- 

 stance by which oxygen can be carried and respiratory and oxidising 

 functions become possible. These considerations will come up with 

 renewed force when we shall speak of anesthetics, especially of 

 those that produce insensibility by abstracting the oxygen from the 

 blood and suspending one of the most important of the organic 

 processes, that of respiration. You will now well understand how 

 a fatal result may ensue from such agents, that greedily appro- 

 priate the oxygen which the blood may have stored up, and which, 

 in addition, still further destroy the integrity of the same in a 

 manner to paralyze its vital function. I have called your atten- 

 tion already to the fact that we can obtain some of those combina- 

 tions in a ciystalline form, to wit: the prussic acid, the carbonic 

 oxide, and the nitric oxide, haemato-crystalline. These combina- 

 tions are far more stable and far more difficult to disassociate than 

 the oxyhaemato-crystals. 



"These changes are faithfully registered in most instances, and 

 we will, farther on, see what great value spectral analysis has in 

 forensic medicine. 



PKEPARATION AND MOUNTING OF FERNS. 



J. D. KING. 



I HE selection of the fern is all important. It should be of 

 -*- robust growth and free from dirt, for a dirty fern is hard 

 to clean. If not fully ripe the spores will be shininken and without 

 character; if over ripe, the spores will not be there. If selected 

 from an herbarium, it must not have been poisoned, for poisons will 

 be likely to interfere with staining. 



Have in readiness a few wide-mouthed bottles that will hold 

 about an ounce. Morphine bottles are excellent. Carefully select 

 the best pinnae and soak them in a bottle of alcohol and water, half 

 and half, till perfectly saturated; this will give the bleaching fluid 

 a chance to take hold more uniformly. If to be kept some time add 

 one foiu-th part alcohol to prevent moulding. It i:!> best not to put 

 but one kind in a bottle if wanted for study. 



Note; — In all the processes of preparation keep eveiything per- 

 fectly clean, avoid shaking the bottles, and handle carefully with 

 forceps without touching the sori. 



For bleaching, the following formula is in common use and 

 is all that can be asked. 



