178 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
transformations of matter and energy during assimilation, the problem 
remains metaphysical. 
Animal Life without Bacteria.* — Herren Nuttall and Thierfelder 
have investigated the interesting question whether the presence of Bac- 
teria in the food-canal is necessary to effective digestion. It was, it will 
be remembered, one of Pasteur’s suggestions that the Bacteria usually 
present in an alimentary tract had probably a symbiotic action in 
digestion and absorption. The authors reared a young guinea-pig with 
the utmost — almost indescribable — carefulness. It was born and bred, 
fed and cleansed, without Bacteria. It lived and died a sterilised 
animal. Therefore microbes are not indispensable. 
Monochromatic Colours among Animals.f — Under this heading 
Dr. Simroth discusses in a somewhat comprehensive manner the pheno- 
mena of Colour in organisms. His object is to gather the isolated facts 
on colour which have been disclosed by recent investigations, and to 
attempt to unify them. The conclusion to which his study of the 
subject has led him is expressed in the following somewhat mystical 
terms : — Almost all the monochromatic pigments of organisms have 
originated from a single substance which is closely united to primitive 
protoplasm, and which by its development and modification gives rise 
to the simple prismatic colours ; these colours appear in the order of 
the spectrum, beginning at the red end and passing gradually towards 
the violet. The reason for this course of development is either (1) the 
fact that in geological time the atmosphere was at first such that 
only the red rays of sunlight could penetrate, and that it became gra- 
dually modified so that the others were also able to pass, the gradual 
appearance of the colours being the expression of this gradual succession 
of stimuli ; or (2) the nature of protoplasm is such as to cause it to 
respond differently to the different rays, the result being that there is a 
relation between the molecular weight of the pigment produced, and the 
length of the rays of light which give the stimulus leading to its pro- 
duction. This, in correlation with the (assumed) fact that the pigments 
near the red end of the spectrum have the simplest chemical structure, 
accounts for the gradual appearance of the colours. Both hypotheses 
of course assume that pigment-production is the response of the sensitive 
organism to the stimulus of light, and therefore a considerable part of 
the paper is devoted to proving the direct effect of light and warmth 
on the production of pigment. The discussion especially refers to the 
colours of the shells of the Plankton Mollusca. 
In support of his main thesis Dr. Simroth brings forward three series 
of facts. First, he appeals to the modifications of “ visual purple ” and 
of the chromophanes of the eye to illustrate his view that under the 
direct stimulus of light one colour may be converted into another, 
the change taking place in the order of the spectrum. Next, he dis- 
cusses at some length the pigments of plants, especially the lipochrome 
series. These illustrate both the evolution of colour and the prevalence 
of primitive colouring-matters in relatively simple organisms. Lipo- 
chromes are pigments of low molecular weight, and are especially 
* Biol. Centralbl., xvi. (1896) pp. 123-4 ; Zeitschr. f. physiol. Chemie, xxi. Hel't 
2 and 3, pp. 109 et seq. f Biol. Centralbl., xvi. (1896) pp. 33-51. 
