PROCEEDINGS OF THE SOCIETY. 441 



no reduction and consequent blackening is exliibited, tlie sjiii-al 

 arrangement of the clilorophyll-bands being still jierfectly distinct. 



Mr. Stewart said be did not see that they bad any actual proof 

 tbat the protoplasm in tbe one case was dead and in tbe otber living, 

 especially wben it was borne in mind tbat tbe way in wbicb it was 

 killed was by means of citric acid, a small residual quantity of wbicb 

 be tbougbt migbt bave some effect upon tbe result. 



Mr. Bennett said it was clear tbat tbey wanted more particulars 

 before coming to a definite conclusion, tbougb it was naturally to be 

 supposed tbat all acid bad been removed before tbe tests were 

 applied. 



Mr. Hartog referred to tbe silver staining processes recently 

 described in tbe Journal. 



Mr. Stewart said if tbey wanted to make silver staining a test in tbe 

 case of tbe tissues of living animals it would not always be found an 

 easy tbing to do. In cases of ojDerations tbey could probably get living 

 tissues, but there were many parts wbicb it would be very desirable to 

 test witb, w^bicb could not be obtained until after twenty-four bours 

 from time of deatb, and yet be tbougbt tbat in sucb cases tbe outlines 

 of a cell were as perfectly rendered as if tbey were living. He was 

 afraid tbat unless tbe citric acid were entirely eliminated, it would 

 probably exercise an important influence on tbe results. 



Dr. Matthews felt sure that sucb would be tbe case, for it was 

 well known tbat in photography tbe developing fluids bad been 

 acidified — and this especially by citric acid — for tbe purpose of 

 retarding tbe reduction of tbe silver salt, so tbat tbe results where 

 acid bad been concerned would be very suspicious. Tbe use of 

 alkaline instead of acid prejDarations was tbe secret of tbe modern 

 rapid processes of photographic development. 



Mr. Crisp referred to the views of Prof. Grunow on W. Prinz's 

 paper on Diatoms in Thin Eock Sections (see p. 246). 



Mr. Ingpen read a note on the use of diaphragms, illustrating bis 

 remarks by drawings upon the black-board. The ordinary wheel of 

 diaphragms in general use was, he considered, effective only to a 

 certain extent ; and be gave tbe preference very decidedly to tbe 

 sliding cylinder-diaphragm so largely adopted on the Continent, 

 which was in fact a modification of tbat devised many years ago by 

 Varley, in wbicb double cylinders were used, one working within the 

 otber. Tbe outer one bad a moderate-sized opening sliding up in 

 tbe substage, or in tbe ring provided for tbe purpose beneath tbe 

 stage, until in contact witb the slide. This cylinder was lined with 

 cloth, to facilitate tbe sliding of the second cylinder, having a similar 

 opening in the cap. By the proj)er use of this double cylinder tbe 

 cone of light could be modified in tbe most perfect manner, — in fact 

 it left nothing to be desired. Tbe plate of diaphragms devised by 

 Dr. Anthony, consisting of a series of apertures in a strip of vellum, 

 to be placed immediately beneath the slide upon tbe stage, did not 

 appear to him effective, inasmuch as at tbe position in wbicb it was 



Ser. 2.— Vol. II. 2 G 



