NATURE 



385 



THURSDAY, FEBRUARY 22, 1900. 



A NEW DEPARTURE IN CYTOLOGY. 

 Fixirung, Fdrbung, und Bau des Protoplasmas. 

 Kritische untersuchungen tteber Technik und Theorie 

 in derneueren Zellforschting. Von Dr. Alfred Fischer, 

 a.o. Prof, der Botanikin Leipzig. Mit einer coloristen 

 Tafel, und 21 abbildungen im text. Pp. x + 362. (Jena : 

 Gustav Fischer, 1899.) 



IT is many years since Dr. Routh administered to a 

 youthful aspirant after literary fame the celebrated 

 advice to " verify your references," and no matter what be 

 the branch of learning concerned, the maxim applies, 

 mutatis mutandis, with equal force to all. Certainly no 

 one devoted to science can afford to disregard it, since 

 extracts from the difificult text of nature are hardly less 

 liable to errors of transcription than to those of inter- 

 pretation. And this is especially true in the case of a 

 study such as that of cytology, for not only is the evi- 

 dence difficult to obtain and the degree of its relevancy 

 to a particular problem hard to decide, but its very 

 authenticity is not to be admitted without full proof. 



Prof. Fischer has thoroughly deserved the gratitude of 

 all who are mterested in the investigation of cell pheno- 

 mena, for he has opened up (even if he cannot claim to 

 have originated) a new and fruitful path of inquiry in 

 attacking the very foundations on which our knowledge 

 of cell structure is based. He has, in fact, conducted an 

 extensive investigation into the reactions obtaining 

 between certain well-known proteids (in the widest sense 

 of the term) and the fixatives and stains which are in 

 common laboratory use. 



The importance of this procedure becomes at once 

 apparent on reflecting that protoplasm, when killed, 

 becomes in fact something else, yielding, inter alia, a 

 complex mixture of proteids, and that it is just these 

 proteids which are so grouped in the dead cell as to 

 produce what we term its structure. 



Many of the proteids can be tolerably easily recog- 

 nised and classified, and it is clearly imperative to learn 

 as much as possible about them and their individual 

 reactions with the substances employed to kill or fix 

 the cell contents. It may be regarded as fairly certain 

 that "fixation " really implies the precipitation of sub- 

 stances which, in the living cell, existed under other forms 

 and other conditions. In some cases, e.g. when salts of 

 the heavy metals are used, it is probable that the metallic 

 base enters into combination with some, at any rate, of 

 the proteids, whilst in the case of some other fixatives, 

 such a possibility appears to be excluded. But in what- 

 ever way the precipitates maybe produced, it is obviously 

 a matter of prime necessity to ascertain the extent to 

 which they correspond, in position and in form, with the 

 structural elements of the living cell. An instance in 

 which such a correspondence is probable is supplied by 

 the chromosomes of a dividing nucleus. These bodies 

 can be identified in the living condition, although it is 

 not until after fixing that the finer details of structure 

 become apparent, and for which it would be hopeless to 

 look in the living nucleus. Now it is precisely as to 

 the extent to which we are justified in regarding these 

 NO. T582, VOL. 61] 



details as faithfully reflecting Uving structure that the 

 greatest uncertainty prevails. 



Many persons are satisfied by the comparative uni- 

 formity exhibited in "well-fixed" specimens when pre- 

 pared by diverse methods. But can the criterion of 

 trustworthiness be safely sought in exquisite diflferentia- 

 tion alone, even though a multitude of reagents should 

 conspire to produce it, unless the specific effects of each 

 fixative be thoroughly understood ? Perhaps few reason- 

 ably cautious cytologists, thus pressed, would return ar> 

 immediately at^irmative answer, although they could 

 hardly conceal from themselves the fact that it is too 

 often on the tacit admission of some such postulate 

 that many of the current theories and hypotheses 

 depend. Small wonder then if these should sometimes 

 prove untenable when the soundness of their founda- 

 tions has been insufficiently tested. 



Prof. Fischer devotes the first seventy-two pages of his 

 book to the consideration of the reactions of certain 

 selected proteids {e.g. albumen, albumose, peptone, 

 nuclein) with the reagents commonly employed for kill- 

 ing and fixing the cell contents. The amount of detail is 

 almost bewildering, and, indeed, throughout the book the 

 reader seeks in vain for short and clear summaries of the 

 many lines of argument. 



The results obtained are such as to throw considerable 

 light on the operations of killing and fixing. Some re- 

 agents, e.g. osmic acid, although they rapidly destroy life, 

 do not precipitate the proteids ; and this fact explains 

 why cells killed with osmic acid retain a considerable 

 resemblance to the living condition. But the action of 

 osmic acid in this respect is easily affected by the presence 

 of other substances, e.g. acids, in the cell, whereby further 

 changes may be induced. Other reagents, sqch as acetic 

 acid or alcohol, bring down some of the proteids, the rest 

 being left in solution ; whilst, finally, there are still others, 

 for example, chromic acid or mercuric chloride, which 

 have a far greater fixing {i.e. precipitating) power. 



Again, the nature of the precipitate is often> 

 characteristic : witness the coagulum produced in 

 albumen, nuclein, or nucleic acid by treatment with 

 mercuric chloride ; whereas, if chromic acid be employed, 

 instead, nucleic acid and albumose are both precipitated 

 in a granular form. But the final result is also subject 

 to some amount of modification, depending on the con- 

 ditions of the experiment. Thus alkalinity, acidity, ex- 

 cess of either reagent, may all affect it, though in a way 

 which can be calculated and reckoned with. A consider- 

 ation of no little importance attaches to the fact that, in 

 mixtures of proteids, the individual precipitate-form 

 characteristic of each proteid is still retained when they are 

 thrown down by a fixative, and the bearing of this upon 

 the probability of arriving at a correct understanding of 

 the structure of living protoplasm, from a study of fixed 

 preparations, becomes immediately obvious. Indeed, it 

 is extremely probable that much of the so-called 

 " structure " may turn out to be the mere expression of 

 chemical idiosyncrasy— interaction between proteid and 

 reagent — rather than an instantaneous photograph, so to 

 speak, of the true structure of protoplasm. An example 

 will make this clear. Altmann's solution (consisting of 

 potassium bichromate and osmic acid) produces a very 

 constant appearance in protoplasm, consisting chiefly of 



S 



