Journal of Applied Microscopy. 363 



blood to last for many months. By the addition of chloroform (in the manner 

 above mentioned) that portion of the serum which is not at once used can be 

 preserved indefinitely. When it is desired for use, the chloroform is driven off by 

 placing the serum in a large flask in a water bath, which is kept at a temperature 

 lower than is required to coagulate albumin. I have found 58° C. about right. 

 The passage of a current of air through the serum while in the water bath would 

 materially hasten this step (which ordinarily takes several hours), but it is 

 impracticable on account of the viscid nature of the material, owing to which the 

 current of air soon converts the serum into a mass of bubbles which completely 

 fill the flask and pass out through the aspirating tube. Transferring the serum 

 to a clean flask about every twenty minutes will somewhat hasten this process. 

 Freedom from the characteristic odor of chloroform indicates its complete 

 evaporation, and the serum should not be used until this point is reached. 

 Further manipulation of the chloroform-preserved serum is identical with that 

 employed with the fresh product. Ernest C. Levy, M. D. 



Bacteriologic Laboratory, Medical College of Virginia. 



METHODS IN PLANT HISTOLOGY. 



Charles J. Chamberlain. 



III. 

 KILLING AND FIXING AGENTS, 



In this short account, only the reagents which are at present considered 

 most valuable for botanical work will be considered. Probably no process in 

 microtechnique is in more urgent need of improvement than this first step of 

 killing and fixing. Nearly all of our formulae are merely empirical, for very few 

 botanists are expert chemists, and those who have the requisite knowledge of 

 chemistry are interested in physiological problems rather than in microtechnique. 

 The principal ingredients of the usual killing and fixing agents are : alcohol, 

 chloroform, chromic acid, acetic acid, osmic acid, formic acid, picric acid, sul- 

 phuric acid, platinum chloride, corrosive sublimate, and formalin. We shall 

 consider first 



THE ALCOHOLS. 



a. 95 per cent. Alcohol. — This is in quite general use for material which 

 is needed only for rough work. It is ex,tremely convenient since it kills, fixes, 

 and preserves at the same time and needs no changing or washing. It really 

 has nothing to recommend it for fine work. It causes protoplasm to shrink, but 

 cell walls usually retain their position, so that 95 per cent, alcohol will do for free- 

 hand sections of wood and many herbaceous stems, but even free-hand sections 

 of tender stems, like young geraniums and begonias, will look better if better 

 reagents are employed. Alcohols weaker than 95 per cent, are not to be 

 recommended as fixing agents, although 70 per cent, alcohol or even 50 per 

 cent, will preserve material for habit work. 



b. Absolute (lOO per cent^ Alcohol. — This is a good killing and fixing 



