April 9, 1896] 



NATURE 



531 



will doubtless prove of special interest, giving, as it 

 does, a concise account of the history of researches 

 commenced over a hundred years ago, which prepared 

 the way for the advent of Pasteur, and which have 

 conducted Hansen on to his special line of investigation. 



Of great importance in all bacteriological researches is 

 the individuality of bacteria and the variations which 

 may be introduced by suitable means in their morpho- 

 logical and biological character. But whilst the im- 

 pressionable nature of bacteria renders their education so 

 particularly attractive, it also complicates in divers ways 

 their successful investigation. Now Hansen has been 

 led to devote a great deal of attention to the varia- 

 tions which are inducible in yeasts, in consequence 

 of the suggestion that the disease yeasts, so undesirable 

 to the brewer, may in reality only be degenerate forms 

 of the true brewery yeasts, and that, therefore, the intro- 

 duction of pure cultures cannot ensure the absence of 

 these malignant forms. But Hansen states that although 

 he has studied for many years the cultivation of pure 

 yeast on a large scale, he has never seen any signs of 

 the brewery yeasts developing forms like those charac- 

 teristic of disease yeasts, that on the contrary, under the 

 conditions obtaining in the brewery, they always retained 

 their specific character ; and he concludes by saying, " the 

 theories of the degeneration and transformation of yeast 

 have thus, in this respect, proved to be quite untenable." 



Yet irregularities do occur in the brewery yeast itself 

 which cause great annoyance to the brewer, and in most 

 cases there is no clue to their cause. 



That yeasts, like bacteria, are capable of artificial 

 modification, has been repeatedly shown by Hansen. 

 Thus he found that yeast grown in aerated wort behaved 

 normally in the brewery as regards clarification and 

 attenuation, whilst that grown in non-aerated wort lost, 

 for a time at least, these functions. Again, on sub- 

 mitting a yeast, Sacch. Pastorianus /., to particular 

 conditions, it completely lost its power of forming spores, 

 whilst at the same time its capacity to produce films in 

 old wort cultures disappeared. 



It is obvious of what great importance is an intimate 

 knowledge of the conditions which are able to modify 

 the character of yeast cells, for, even with pure cultures, 

 the brewer is yet unable to perfectly manipulate the 

 working of his yeast, although the elimination of un- 

 friendly varieties has materially lightened his difficulties. 



Recently the old question has been revived by Juhler 

 and Jorgensen as to the origin of yeast cells, and it is 

 yet a question to which we have no final answer whether 

 they are to be regarded as independent organisms, or 

 only forms of development of the higher fungi. Fifty 

 years ago the latter view was held by Bail, Hoffmann, 

 and others, but at present Juhler's and Jorgensen's 

 observations on the development of yeast cells from the 

 Aspergillus oryzce have not been confirmed, for Klocker 

 and Schionning repeated their experiments, but failed to 

 observe the development of yeast cells. 



Until we shall be in a position to trace out the parent- 

 age of yeast cells, we cannot aspire to arrive at a com- 

 plete understanding of the conditions which determine 

 their individual characteristics. The same difficulty 

 faces the student of bacteria ; whether the differences, 

 sometimes so slight, but, as far as our means of observa- 

 NO. 1380, VOL. 53] 



tion at present extend, apparently quite constant between 

 otherwise such similar forms of bacteria, are funda- 

 mental or produced from the same form by conditions 

 of which we have no knowledge, is still one of the 

 problems of which we have no satisfactory solution. 



Just as Hansen has been able to present us with a form 

 of yeast from a spore-producing parent which will not 

 form spores, so, for example, Roux has introduced us to 

 sporeless anthrax ; whilst in bacterial fermentations, Percy 

 Frankland has shown that by suitable treatment the pro- 

 geny of a fermenting organism can be made to yield up 

 its power of fermenting particular solutions, and that only 

 by resorting to special treatment can its fermentative 

 powers be restored to it. 



In the case of the sporeless yeast, and sporeless 

 anthrax, and the non-fermenting bacteria, it would be 

 impossible, on casually meeting with them without a 

 previous acquaintance with the facts, to avoid regarding 

 them as different species of yeast and bacteria from the 

 familiar spore-producing yeast, and anthrax, and ferment- 

 ing bacteria respectively, yet we know as a fact that they 

 are in reality but variations from the parent form in each 

 instance. 



It is obvious, therefore, how important is a knowledge 

 of the pedigree of these minute particles of living matter 

 to enable us to rightly appreciate their character, reckon 

 upon their conduct, and determine their claims to be 

 regarded as separate species. 



Prof Hansen is at present engaged in preparing a 

 special account of his researches on these variation 

 phenomena in yeast, and the conditions which control 

 them ; and the work cannot fail to prove of great im- 

 portance not only to the practical brewer, but to all 

 interested in the study of micro-organisms. 



PALAEONTOLOGY AT THE BRITISH 



MUSEUM. 

 Catalogue of the Mesozoic Plants in the Department o) 

 Geology, British Museum {Nat. Hist.). The Wealden 

 Flora. Part II. Gymnospermce. By A. C. Seward, 

 M.A., F.G.S.. 8vo. Pp. xi + 259; pi. 20, and 9 

 illustrations in text. (London, 1895.) 

 Catalogue of the Fossil Fishes in the British Museum 

 (Nat. Hist.). Part III. Containing the Actinopterygian 

 Teleostomi of the orders Chondrostei (concluded), Pro- 

 tospondyli, .Etheospondyli, and Isospondyli (in part). 

 By A. Smith Woodward, F.G.S. Svo. Pp. xlii -f 544 ; 

 pi. 18, and 45 illustrations in text. (London, 1895.) 

 ''T^HESE two catalogues, the last additions to the long 

 -•- series of palasontological monographs published by 

 the Geological Department of the British Museum, testify 

 to the value of the work there done under the super- 

 vision of Dr. Woodward. The two volumes illustrate, 

 moreover, the strikingly different points of view from 

 which palajontological problems are regarded. Mr. 

 Smith Woodward's catalogue is zoological in its aims 

 and methods, while in Mr. Seward's, though the methods 

 are biological, the most generally interesting results are 

 geological. 



The first volume of Mr. Seward's catalogue of the 

 Wealden plants described the AlgcC, Characeit, Equi- 

 setinit, and Filicin;e ; the present volume concludes 



