HARDWICKE'S SCIENCE-GOSSIP. 



"5 



species formerly included in that class are included 

 here, while a few have even been claimed from the 

 animal kingdom. As regards the boundary between 

 the Schizomycetes and the Algre, the discriminating 

 test is merely the want of chlorophyll. The order 

 of Alga? most nearly allied to these fungi is the 

 Phycochromacepe, which live in pure water or in 

 damp localities ; like other Algce, they do not require 

 the presence of organic matter in the moisture in 

 which they flourish ; they produce no striking 

 decomposition therein ; and they soon perish in a 

 putrefying fluid. The Schizomycetes, on the 

 contrary, live solely on the decay of organic matter ; 

 they produce very marked decompositions in the 

 fluid which they inhabit ; they revel in putrefying 

 substances, and cannot exist in pure water. 



In regard to the distinction of the Schizomycetes 

 from the Infusoria to which they make the nearest 

 approach, the Monadina, it cannot be said that there 

 is yet known any absolute test. Some of the mouth- 

 less monads so closely resemble Bacteria that the 

 possibility is that before long they will be classed in 



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Fig. 79. — Bacillus tiiberculosus, from human sputum. 

 a X 1200 ; b X 1500. 



the same group. It is just here that part of the shadowy 

 boundary between the animal and vegetable king- 

 doms runs, and that boundary may never be more 

 definitely fixed. 



There is still another question which deserves 

 mention, and that is, are the forms described above 

 true species ? A great deal of useless talk has been 

 wasted upon this subject : many persons argue from 

 a preconceived idea as to the limits of species ; 

 others from some fanciful notion as to the number of 

 species which ought to exist ; others again reason 

 that forms frequently found in company with one 

 another, or agreeing in some one point, such as 

 colour, must be phases of the same species. Upon 

 the first two "arguments" nothing need be said; 

 concerning the last it may be observed that, however 

 useful co-occurrence or similarity may be in suggest- 

 ing the possibility of genetic connection, it yet falls 

 far short of the probability which science requires. 

 To prove that one form of life is merely a phase in 

 the development of another, one thing, and one thing 

 only, is sufficient ; the one must be traced into the 



other. Professor Ray Lankester has classed a great 

 many bacterial and monadic forms together as one 

 species, Bacterium rubescens (for references see 

 Cohnia roseo-persicina, vol. xviii. p. 200), merely 

 because he found them all together in the same 

 habitat, and they present certain points of similarity, 

 especially in colour. But this is unsafe, nay un- 

 philosophical. If it can be shown that one cell of 

 Cohnia, sown in a suitable fluid, produces all these 

 various forms without the intervention of any other 

 germ, then and not till then can his contention be 

 admitted. 



The warning of previous cases of the same 

 character is too plain to be neglected. Professor de 

 Bary described (Beitrage zur Morph. und Phys. der 

 Pilze, 2nd series, pp. 1 3-24) various mucorine forms 

 as phases in the life-history of Mucor Mucedo ; and 

 succeeding botanists, deferring to so high an 

 authority, repeated the error. But Professor de 

 Bary's experiments were made in the ordinary way, 

 and every one who has examined the Mucorini knows 

 the vast abundance of their spores and the impossi- 

 bility of excluding them from an ordinary culture. 

 Mons. van Tieghem, however, sowed one single 

 spore of each form, such as Thamnidium or Chaeto- 

 cladium, in a drop of water or other liquid : in every 

 case where the absence of any extraneous spore was 

 satisfactorily ascertained, the sown spore reproduced 

 its parent form and no other, and this process was 

 continued for many generations.* Professor de 

 Bary himself now admits that his previous con- 

 clusions were unfounded (Beitrage, 4th series, p. 1). 

 In the same way, as soon as experiments were de- 

 vised by which the progeny of one bacterial cell could 

 be ascertained, it was found that there was no longer 

 that intermixture of various forms which had 

 previously confused and misled observers. Micro- 

 coccus produced nothing but Micrococcus, Bacterium 

 nothing but Bacterium. ( Vide Koch's experiments.) 

 To my mind it certainly seems most rational to 

 assume that every form which has not been shown 

 to be capable of being produced by another form is 

 a distinct species, until the contrary is proved. 

 Certain writers, however, are captivated by the 

 opposite view, and seem to regard themselves as 

 adopting a higher scientific position when they 

 advocate the union of distinct forms, upon no 

 better ground than that when one is sown others 

 will appear. But this is to ignore the minuteness 

 and omnipresence of the reproductive germs of all 

 these lowly forms of life. The very diversity of the 

 species which are found at different times in the 

 ordinary culture of any one throws suspicion on the 

 hypothesis of their genetic connection. We arrive 

 then at the conclusion that, for the present and until 

 the contrary is proved, all the species enumerated 



* "Recherches sur les Mucorinees,"par Ph. van Tieghem et 

 G. Lemonnier, pp. 18, 48, etc. Brefeld in " Botanische Unter- 

 suchungen fiber Schimmelpilze" arrives at the same result. 



