158 American Quarterly Alicroscopical Journal. 



I beg not to be understood as intimating by this remark, that in 

 this case the slight difference of aperture would hold good for any- 

 notable difference in the performance of the lens, in comparison with 

 a standard objective of the same kind — which is not at all my opinion. 



I must consider as of much greater importance for the result of a 

 given trial that the length of the tube, in observing with the oil- 

 immersion, be accurately adjusted according to the direction in Mr, 

 Zeiss's circular ; and that for observations with oblique light the oil 

 be applied which Mr. Zeiss prescribes for oblique light, and for obser- 

 vations with central light the oil prescribed for central light. 



Jena, Dec. 14th, 1878. Dr. E. Abbe. 



NOTES. 



— In a recent letter to the editor, Mr. W. H. Bulloch, of Chicago, 

 writes : " If it is not too late, will you put a notice in your next number 

 that one of my ' Congress ' stands will be on exhibition at your office ?" 

 This explains itself, and any reader who is interested will be welcome 

 to examine this stand as soon as it arrives. It is the rival, and the only 

 one, of the " Centennial " of Mr. Zentmayer ; and as one of the latter is 

 also in this city on exhibition, we are glad to afford this opportunity 

 for their comparison. 



— Professor Engelmann thinks that the contents of the contractile 

 vesicles of the Infusoria are expelled into the surrounding water. He 

 was not able to determine whether any water was taken in during ex- 

 pansion, but believes not. 



— White of egg is now recommended as an imbedding medium for 

 soft tissues. The material to be imbedded, freed from alcohol, is placed 

 in the albumen in a little paper box, and the whole exposed to heat 

 until it becomes hardened, then placed in alcohol as usual. The sec- 

 tions should be passed through oil of cloves into balsam. The albumen 

 thus becomes clear and transparent. 



— It is stated that a cold 5-6 per cent, solution of borax will remove 

 all the red, blue, purple, or violet coloring matters from vegetable cells, 

 leaving the green chlorophyll intact. 



— The study of bacteria promises to be greatly aided by the recent 

 processes for staining them. The most elaborate process, and the one 

 giving the best results, is that of Dr. Koch, of Wollstein. In brief, his 

 process is as follows : A drop of the fluid containing bacteria is placed 

 on a slide and dried in a very thin layer. For simply preserving the forms, 

 a solution of one part of potassic-acetate in two parts of water, is added, 

 and a cover cemented on. To stain them, aqueous solutions of methyl- 

 violet, known to the trade as B B B B B, and fuchsin are preferred, al- 

 though almost any anilin colors will act. For photographic purposes, 



