680 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
“ (2) The diffraction-spectra are, according to Abbe (in monochro- 
matic light), set up as the real images generated by the system, and due 
to the bright parts of the virtual diffracted appearances generated by 
the objective structure in the image-forming infinitely distant planes. 
“ (3) The stereometric place for equality of phase is not so much 
the image-forming focal plane, as a spherical surface concentric to tho 
image-point and generated by the image-forming focal point. 
“ (4) The direct primary maximum lies at the image-forming focus, 
but the deflected secondary maxima do not lie in the image-forming focal 
planes ; the collective diffraction-spectra are not aplanatic images. 
“ (5) The diffraction-spectra do not lie generally on a spherical 
surface, and even if they do, then this spherical plane is generally not 
concentric to the image-focus; generally the ray-paths have not equal 
distances between the diffraction-spectra and the image-focus, i.e. the 
diffraction-spectra are not in the same phase. 
“(6) If the objective is aplanatic, then the locus of the real diffrac- 
tion-spectra is formed with unequal phase by means of a spherical surface 
concentric to the image-focus ; consequently it is easily understood that 
the normal microscopic image is erected at a definite point of the optical 
primary axis (i.e. at the centre of the spherical surface), and not in any 
desired point, so that the diffraction-spectra lie with equal phase in the 
focal plane, 
“(7) When the surface (generated by the image-forming focus) is 
of such a kind that it contains the collective diffraction-spectra in the 
same phase, I call it the ‘ wave-surface 5 ( Wellenflache ). This ‘wave- 
surface ’ is constant for the aplanatic arrangement of the system.” 
B. Technique. * 
Cl) Collecting- Objects, including Culture Processes. 
Artichoke as Nutrient Medium. j- — M. M. Roger recommends arti- 
choke as a nutrient medium, as many bacteria and yeasts grown on this 
substratum exhibit a characteristic appearance. With some species the 
infection-site assumes a green hue, with others it remains uncoloured. 
B. subtilis forms a deposit in 24 hours, the subjacent substratum being 
coloured green. Anthrax does the same in 3-4 days. Typhoid has no 
action on the substratum. B. prodigiosus when incubated imparted the 
green staining, though the red pigment did not form. At room tempe- 
rature the cultures of B. prodigiosus exhibited the red colour, while the 
green staining was absent. 
The author suggests that the green pigment is due to the oxidation 
of some constituent of the artichoke owing to the (vital ?) action of the 
microbes. That it is an oxidation process is obvious from the fact that 
when oxygen is excluded, the green pigment is not formed. The pig- 
ment is soluble in water, insoluble in alcohol, chloroform, and ether. 
Acids turn it red, while bases restore the green colour. 
* This subdivision contains (1) Collecting Objects, including Culture Pro- 
cesses; (2) Preparing Objects; (3) Cutting, including Imbedding and Microtonies ; 
(4) Staining and Injecting; (5) Mounting, including slides, preservative fluids, &c. ; 
(6) Miscellaneous. 
f C.R. Soc. Biol., v. (1898) pp. 769-71. 
