158 SUMMARY OF CURRENT RESEARCHES RELATING TO 



indirectly, the purity of the air in the fermenting rooms, &c., and the 

 important part it phxys in the analysis of water, he refers to the determina- 

 tion of the quality of the yeast as by far the most important use of the 

 Microscope to the brewer. " The presence or absence of certain bacteria 

 is of vital importance, as it is these foreign organisms that cause the un- 

 healthy fermentations that used to perplex brewers so much ; but which 

 (thanks to such men as Pasteur, Huxley, Tyndall, Lister, Budd, and others) 

 they are now learning to detect and remove. The germs most frequently 

 found contaminating yeast are JBaderium lactis, B. aceti, and B. amylo- 

 hacter, and it is these three that are familiar — too familiar — to most 

 brewers. We now know that a healthy yeast-cell should not be larger 

 than 1/2000 in. in diameter, and as a micrometer is an indispensable 

 adjunct to every brewer's Microscope, the size is easily measured. We 

 know that the absence of any vacuole in the cell denotes the plant to be 

 too young, and not fit to induce a vigorous fermentation, and that the 

 presence of more than three vacuoles and a shrivelled cell, at once points 

 out the yeast to be too old. We learn from the presence of an undue 

 amount of lactic and other ferments, when it is time a change of yeast 

 was sought, and the ' change ' having arrived, we can examine it before 

 using, and determine the age and quality of the purchase." 



The author adds that as this is intended for non-professional readers, 

 he will not enter into any lengthy detail. " This is merely to show that, 

 whilst the Microscope affords a most pleasing recreation to many men, and 

 a deep life-study to others, its value to a tx'ader is not the least of its 

 uses. The growing taste for microscopical research amongst men is a sure 

 sign of the intellectual age in which we live ; and now that a good instru- 

 ment can be purchased for such a small outlay, it behoves all men to get 

 as deep an insight as possible into the wonders of the world around us." 



(8) Bibliograpliy. 

 American Society of Microscopists. 



[Recommeudation of Washington for the next meeting.] 



The Microscope, VI. (1886) p. 273. 

 Behhens, W. — Berichtigung. (Correction.) 



[Angry remonstrances as to his not having been furnished with the earliest in- 

 formation as to the new glass and objectives, instead of having to take his 

 account of them from this JournaL] 



Zeitschr. f. Wiss. Mikr., III. (1886) pp. R93-4. 

 Bolton, Thomas, F.E.M.S. 



[Grant of a Civil List pension of 50/. per annum.] 



Midi. Naturalist, X. (1887) pp. 22-4. 

 BosTwiOK, A. E. — On a means of determining the Limits of Distinct Vision. 



[" Let a ruler lean against the shade of a lamp ; place the eye so near that the 

 image is necessarily blurred, and, moving the edge of a sheet of paper back and 

 forth before the eye, step slowly backward till apparent motion of the object 

 ceases ; continue the backward movement until the object begins to recede 

 slightly from the screen ; the space where there was no motion is that in which 

 alone distinct vision is possible. Of course, every effort must be made to 

 accommodate the focus of the eye to the object during the whole experiment. It 

 is a more difficult task than one thinks, to decide by simple judgment whether 

 an object is distinctly seen or not, except it be much blurred. If the image is 

 fairly distinct, most people will suppose it to be perfectly so. The test described 

 above never fails to thow whether or not the judgment is correct."] 



Science, VIII. (1886) p. 232 (1 fig.). 

 Btjbbill, J. T. — Bacteria and Disease. 



[Presidential Address to the American Society of Microscopists, 1886.] 



St. Louis Med. and Surg. Journ., LI. (1886) pp. 131-45. 

 Christian, T. — [Slide for testing Astigmatism of the eye.] 



["Mr. Christiun exliibited an interesting test slide (his own preparation) in- 

 geniously mounted, with a view to discover any astigmatism of the eye. It 

 consists partially of diatoms of the Navicula shape. If the eye of the observer 



