116 



KNOWLKDGK. 



April. 1915. 



invited Prt Minchin to occupy the chair, and 



gave in- annual address. The title wai "The Biological 

 ption "i Individuality. " Professor Dendy observed 

 that probably most ol us think that we can recognise 

 and define an individual, but that, though this is 

 true >>t an individual man or dog, or an individual 

 oak tree 01 cabbage, ii we cans- our investigations below 

 the mii (ace, we find many cases thai are not a little puzzling, 

 and the purpose ol the address "as to enquire whether it 

 i- really possible to frame a definition oi individuality, 

 from a biological point of view, that will be of general 

 applicability throughout the animal and vegetable king- 

 doms. There appeared to be two main paths by which the 

 problem could be approached : the morphological and the 



physiological, On the one hand, it was possible to enquire 

 what eonsitntes a perfect individual from the point ol view 

 of structure; and. on the other, as to what constitutes 

 ,tn individual as regards function. In the case of the higher 



animals the question might also be approached in a third 

 way, namely, from the psychological standpoint. The 

 -I i in ture of various unicellular and colonial organisms, and 

 of many of a higher development, was discussed, and diffi- 

 ( nines which arise in deciding their claim to individuality 

 commented upon. Two examples from the higher class 

 may be given. Taking a colonial organism — say an obelia 

 or sertularia — the fertilised egg develops into a single 

 individual, but that individual does not stop developing 

 when it has attained its full growth : it branches out and 

 produces other individuals by a process of budding, and in 

 the colony thus formed it is impossible to say where one 

 individual ends and another begins, though it may be quite 

 possible to say how many individuals there are altogether 

 by simply counting heads. Perhaps the most interesting 

 case was one which well sums up difficulties occurring, 

 especially from the physiological point of view. It may be 

 given in Professor Dendy 's own words : " Many of the 

 higher animals, though they do not form colonies in the 

 morphological sense, have the habit of living together in 

 social communities, which we may regard as colonies of 

 completely separated individuals. The Honey Bee is a 

 familiar example. In a hive of Bees we find individuals 

 of three kinds, easily distinguished from one another both by 

 habits and by structural peculiarities. The Queen is a per- 

 fect female, and is alone capable of laying eggs. The 

 ordinary workers are imperfect females, which have sacri- 

 ficed the power of reproduction, and concentrated their 

 energies upon the collection of food and other important 

 services necessary for the welfare of the community as a 

 whole. The Drones are males : they do no ordinary work ; 

 their sole function is to fertilise the Queen. None of these 

 different kinds of individuals could live a really independent 

 life : they are all mutually dependent upon one another. 

 The morphologist, however, could not refuse to regard 

 them as separate individuals, and probably the physiologist 

 would agree with him. But, if we are to be strictly logical, 

 from the physiological point of view the complete individual 

 can be nothing less than the entire community." . . . 

 " It appears, then, to be hopeless to seek for any 

 biological definition of individuality that can be applied 

 to more than a very limited number of cases : we have 

 constantly to modify our ideas on the subject as we 

 . pass from one group of organisms to another, and every- 

 thing depends upon the point of view." ..." Individu- 

 ality, though a very real, is a very elusive, phenomenon, 

 and one which perhaps lies outside the legitimate domain 

 of the biologist. We can do little more than collect the 

 remarkable facts that confront us so frequently in the 

 course of our investigations, and hand them over to the 

 philosophers to deal with as best they can." 



PHOTOGRAPHY. 



By Edgar Senior. 



PAPIER MINERAL.— One of the most useful of photo- 

 graphic materials is a form of tissue paper, known as 



" papier mineral," readily obtainable at most photographii 



dealers. A sheet attached to the glass side ol a negative 



affords great facilities for alterations and improvements 

 m negatives generally, as it may be worked upon in various 

 ways to modify the effect produced in printing. In land- 

 i ape work, the appearance of distance may be made more 

 real by its means ; and it is also one oi the greatest aids 1 < • 



successful vignetting. The opening in the vignetting mask, 

 if covered with a pine- oi "papier mineral," will enable 

 a much softer and a more easily controlled vignette to be 

 obtained, and at the same time allow also advantage to be 

 taken of direct sunlight in printing, should it be necessary ; 

 and in a variety of ways it will assist the photographer 

 to improve his work. In almost all cases where ground glass 

 is useful this semi-transparent paper can be made to take 

 its place ; thus a piece stretched over plain glass can be 

 used as a focusing screen, should the latter get broken when 

 travelling. Then, again, in portraiture " papier mineral " 

 is useful for covering light movable screens or pasting 

 direct on to a skylight, and sunlight may be filtered through 

 it, and effects produced, which are in every way satisfactory ; 

 and on dull clays it does not obstruct the light sufficiently 

 to appreciably lengthen the time of exposure. When using 

 " papier mineral " as a means of obtaining the effect of 

 atmosphere in the print from a landscape negative by- 

 causing the more distant objects to appear more or less grey — 

 " the greater the distance the greyer the objects should 

 appear " — it must not be forgotten that the lights of distant 

 objects are grey compared with those in the foreground, 

 and care must be taken that these distant lights do not 

 appear too strong in the print. To obviate this, resort is 

 sometimes made to strengthening those in the foreground 

 and middle distance, but this requires to be done very care- 

 fully. Thus, by means of tissue paper, it is possible to 

 produce in the photographic print an effect more nearly 

 in accord with nature than the negative alone would be 

 able to render, owing to its imperfect gradations. If the 

 photographic process gave a true rendering of all objects 

 depicted, then resort to any such means would not be neces- 

 sary ; but as it usually falls short of doing so, any means 

 may be considered legitimate that will enable the desired 

 end to be obtained, and produce the effect that a perfect 

 process would do. In all cases, however, care must be taken 

 not to overdo it. 



DEVELOPMENT WITH EIKONOGEN.— The develop- 

 ing properties of this substance were first pointed out in 

 1881 by Professor R. Meldola, who prepared the acid 

 from which the sodium salt was afterwards obtained, 

 and introduced under the name of "eikonogen," a name 

 derived from the Greek, and signifying "image-producer." 

 In its pure state eikonogen is a white substance. It is 

 the sodium salt of amido-^-naphtholsulphonic acid, its 

 constitution being expressed graphically as follows : — 



CH 



CNH„ 



HC <^\ C /\ COH 



NaS'O.C 



CH 



^CH 

 CH 



or doH.OHNHjSOsNa.SHX) 



The substance is somewhat sparingly soluble in water, 

 but dissolves more readily in the presence of alkalies 

 Sodium sulphite is the best preservative, and acids added 

 to the solution cause the free acid to be precipitated in the 

 form of white needles. It can be recrystallised from 

 solution in sodium sulphite. Eikonogen as a developer 

 was patented in 1889 by Dr. Andresen, of Berlin. It is 

 very quick in its action, and produces soft negatives of 

 a very fine colour, and on this account it is invaluable 

 in portraiture. It is also specially suited for instantaneous 

 work, and it has been claimed that it will give more detail 



