October, 191j 



KNOWLEDGE. 



305 



may be washed and 

 used several times, but 

 it ought to be boiled 

 before its use a second 

 time. The whole 

 answers almost every 

 recjuirement of even 

 the most exacting, and 

 its cheapness is its 

 smallest recommenda- 

 tion. The ordinary wire 

 ring and gauze funnel 

 with a small tube at the 

 bottom is, as everyone 

 knows who has used it, 

 a mere inconvenient 

 plaything, and for sew- 

 age effluents .all but use- 

 less. This apparatus, 

 simple as it is, answers 

 all but every scientific 

 requirement. It catches 

 an exceedingly large 

 proportion of bacterial 

 organisms, and for 



ordinary pond life it is an almost perfect 

 filter for very few creatures get through. 



For marine life, one of a much larger size 

 may be used and the dredge emptied into 

 it, but in this case it is best made without 

 openings in its side, and a wet string must 

 go tightly round the bottom not less than 

 three or four times and be securely fastened. 

 One a foot wide and high is a good size. 

 It need not have a hook on the side, as a 

 bucket will, of course, be used into which to 

 empty the filtrate. A quart enamelled jug 

 makes a convenient ladle, and it must be 

 remembered that marine life above all 

 requires plenty of room, and that large 

 glass cloches must be employed if an 

 aquarium is not used. Finger glasses, which 

 do well temporarily for pond life, are 

 utterly inefficient for any marine gatherings 

 except those derived from the small rock 

 pools. 



My own apparatus cost me thirteenpence. 

 My old apparatus, which cost about five 

 shillings, is now used as a pickling jar. a 

 purpose for which it is seemingly far better 

 fitted than that for which it was primarily 

 designed. People no 

 longer ask me whether 

 I have been catching 

 ■■ minners," in fact they 

 see nothing, not even a 

 collecting stick, and 

 hence one is looked 

 upon as slightly more 

 sane than heretofore — 

 so easily are reputa- 

 tions for wisdom ac- 

 quired, I am quite 

 certain that once used 

 the apparatus will 

 never be replaced, at 

 any rate not by any 

 other at present in the 

 market. 



E. Ardron 



HUTTON. 



SPOTS IN PHOTO- 

 GRAPHIC PRINT- 

 ING PAPERS.— Ob- 

 jects of much interest 

 to the microscopist are 

 the minute metal spots 



FlGURi; 429, 



Figure 430. 



which occur in various kinds of photo- 

 graphic papers, chiefly the printing-out 

 varieties, coated with gelatino-chloride and 

 collodio-chloride emulsions. 



If the sensitiveness of a sheet of paper be 

 removed by the usual fixing process and 

 the surface examined under a low power — 

 a one-inch objective is sufficient — one will 

 frequently find a few .spots embedded in or 

 resting upon the film. The larger ones can 

 be detected by unaided sight, but the more 

 minute forms require optical assistance to 

 locate them. 



Many of the spots have no definite shape, 

 but occasionally most beautiful designs occur 

 consisting of a net-work of filaments, 

 radiating from a dense nucleus. They are 

 doubtless the result of crystallisation of 

 one of the various metals entering into 

 the composition of the emulsion— probably 

 the silver — as the formation of the filaments 

 bears some resemblance to the well-known 

 shape of silver crystals. 



These "' silver trees " are generally caused 

 by metallic impurities in the paper itself as, 

 in several cases, the 

 nucleus was found 

 embedded in the fibres 

 on the surface ; small 

 particles of metal or 

 other reducing agents 

 might also occur in the 

 baryta substratum 

 upon which the emul- 

 sion is usually coated 

 and, in any case, an 

 action reducing the 

 chloride to the metallic 

 state would result. 



The sizes of the spots 

 are sometimes as large 

 as two millimetres in 

 diameter and the forms 

 range from a few strag- 

 gling branches to a vast 

 network of beautiful 

 design. Those pro- 

 duced upon the collo- 

 dion film are character- 

 ized by the delicacy of 

 the filaments which can 

 be traced to the exact point in the nucleus 

 where the action commenced ; in the case 

 of the gelatine film, the filaments are much 

 thicker and the nucleus is generally a larger 

 mass than in the collodion variety. The 

 difference may be due to the dissimilarity of 

 the gelatine and collodion or to a combina- 

 tion of metals forming the crystals. 



Figures 427 and 428 show types found in 

 the collodion film, and are magnified eighty 

 and fifty times respectively, the photographs 

 being taken by reflected light, which is the 

 best method of illumination for examining 

 this variety. 



F'igures 429 and 430 are typical of those 

 which occur in gelatine film magnified 

 ninety and ninety-five times respectively; 

 in these instances transmitted light was 

 used, as reflected light fails to reveal the 

 narrow intersections between the filaments. 

 The colour of the filaments is always 

 light brown when they are embedded in 

 the film, and most of the collodion variety 

 occur in this position : in the case of the 

 gelatine papers, most of the crystallisation 

 takes place upon the surface. With both 



