386 



NATURE 



[February 22, 1900 



well-defined granules lying in a spongy framework. But 

 a closely similar image can also be produced by sub- 

 stituting a mixture of serum-albumen and deutero-albu- 

 mose for the protoplasm, and it is at least open to 

 suspicion that the appearances are evoked in the proto- 

 plasmic corpse, as they certainly are in the mixture, by the 

 ■definite action of the chemicals employed. 



But, although it may be conceded that the study of 

 fixed (and stained) preparations is, after all, largely one 

 of the structure and relations of precipitates, it would be 

 going a deal too far to regard this as at once invalidating 

 the results which have been arrived at by a careful use 

 of histological methods. Thus in many cases it will 

 readily be admitted that the precipitation-figures indicate 

 and correspond with regions of active and special meta- 

 bolism within the cell. It may well be, however, that we 

 shall find ourselves on safer as well as on more fruitful 

 ground in investigating the nature of the substances in- 

 volved in cellular activity rather than in studying the 

 minute details of structure. Some, indeed, have already 

 regarded as illusory many of these appearances which 

 now would seem to have been summoned into existence 

 by the mere act of coagulation or precipitation. 

 Zacharias, as well as Fischer, though working on 

 different lines, has shown how much valuable knowledge 

 can be obtained by micro-chemical methods, and these 

 are still in their infancy. 



After dealing with fixatives, the author next turns his 

 attention to staining, and in particular to the effects of 

 the aniline dyes. It is obviously impossible to discuss 

 the whole of this complex subject here. Those who are 

 interested in the matter may turn to Prof, Fischer's 

 treatise itself, where they will find an immense supply of 

 further information and facts. 



The authof arrives at the conclusion that a chemical 

 (in the ordinary acceptation of the term) interaction be- 

 tween dye and tissue elements is out of the question, 

 and that the process of staining is a purely physical one 

 depending on the " adsorption " or condensation of the 

 dye on the surface of the ultimate particles (micellcc) of 

 the stainable substance. It is pointed out that acid dyes 

 differ in important physical characters, such as solubility, 

 from the basic stains ; and it is argued that these differ- 

 ences, coupled with the physical structure of the body 

 to be stained, will account for the particular colour re- 

 action produced in any given instance. These conclusions 

 will come as a shock to those who have been accustomed 

 to pin their faith on the aniline dyes, and who have seen 

 in " Cyanophily " or " Erythrophily '"' an index of chemical 

 distinction between the various groups of cell-constituents. 

 The evidence brought forward by Dr. Fischer in support 

 of his thesis is based not only on the observations and 

 practice of technical workers ; he has himself contributed 

 an elaborate series of experiments designed to elucidate 

 the phenomena of dyeing ; and if his results are not 

 always free from ambiguity, some margin, as he himself 

 hints, must be left as a tribute to our imperfect acquaint- 

 ance with the objects and processes concerned. Never- 

 theless, so far as the positive evidence goes, it certainly 

 seems to afford confirmation of the physical, rather than 

 the chemical, theory of staining phenomena. 



Following the same plan as that which yielded good 

 results in his investigations on fixatives, the author ex- 

 NO. 1582, VOL. 61] 



perimented with precipitates of known proteids. He 

 finds that no constant relations exist between the staining 

 capacity of a proteid and its power of forming a preci- 

 pitate on adding the dye to its solution. Thus nucleic 

 acid, which takes up basic, but not at all acid, dyes, is 

 only precipitated from solutions by the former. On ^he 

 other hand, albumen, whilst also only precipitated by 

 basic dyes, is stained more especially by acid ones. 



It is very well known that it is essential in the case of 

 certain fixatives {e.g. those containing chromic acid or 

 platinum salts) to carefully " wash out " the superfluous 

 fixative before staming is possible at all. Prof. Fischer 

 uses these facts to support his views, assuming that 

 just as the stain may be adsorbed, so also, in some 

 cases, the fixative may be attracted and held, leaving no 

 place for the stain until it is thoroughly washed away — a 

 process which is often attended with considerable diffi- 

 culty. The same peculiarity of inhibiting staining is 

 shared by sonie other substances, though they may form no 

 precipitate with the dyes employed ; thus tannin, which 

 precipitates basic, but not acid, dyes, impartially inhibits 

 the staining power of them all in proteids saturated 

 with it. Again, although platinum chloride precipitates 

 eosin but not acid-fuchsin, a proteid fixed with this re- 

 agent and not subsequently washed will not take up 

 either dye ; whilst chromic acid, if it be substituted for 

 the platinum salt, although behaving in precisely the 

 same way towards solutions of these dyes., does not 

 hmder their staining at all. 



As might, perhaps, have been anticipated from the 

 author's own standpoint, the fixative used may modify 

 the primary capacity for stains possessed by the pro- 

 teid, but this secondary effect is probably to be con- 

 nected with a changed molecular or micellar form. 



Another argument against a chemical explanation is 

 founded on the behaviour of precipitates of even the 

 same proteid towards mixtures of stains. Precipitates of 

 albumose, for example, which contain granules of various 

 sizes, select the stain according to their bulk, the larger 

 granules taking up and retaining the acid (more rapidly 

 diffusible) dye, whilst the smaller ones are coloured by 

 the basic stain. There seems no reason to suppose that 

 the granules differ chemically inter se, although this 

 objection has actually been raised in other quarters, and 

 Fischer interprets the effect as being due to the difference 

 in solubility, concentration, and rate of diffusibility of 

 the two classes of stains, coupled with the degree of 

 tenacity with which, when once adsorbed, the molecules 

 of dye are retained on the micellae of the proteid. The 

 reversals of stain so frequently met with under these 

 conditions appear also to tell in favour of the physical 

 or mechanical hypothesis. But the author by no means 

 confines himself to a study of simple proteids, he also 

 discusses the bearings of his results on the staining 

 reactions of protoplasm itself. 



Amongst the more interesting of the latter may be 

 reckoned the characteristic differences exhibited by the 

 nucleus of the male and female gametes respectively. 

 Dr. Fischer regards the cyanophily of the male as due to 

 the dense state of aggregation of its substance, and not 

 at all as indicative of a chemical dissimilarity between it 

 and the erythrophil female nucleus. His case is not 

 weakened by the fact that, in those instances where 



