SCIENTIFIC SUMMAKY. 
443 
itself, we know approximately that tke refractive index of diatom aceous 
silex is 1*434 (much below that of quartz), and this is accordingly, for 
diatoms, our neutral point. Although I have said colourless objects mounted 
in a colourless medium become invisible, it is of course equally true if both 
are of the same colour and of the same index. By progressively increasing 
the refractive power of the mounting medium, the diatoms gradually again 
become more and more visible until, as we all know, when mounted in 
Canada balsam (1*540) the coarser species are sufficiently defined for all 
ordinary purposes ; but if we require a still greater departure from the 
neutral point or invisible condition, we must select some other substance of 
still higher refractive power. This we find in bisulphide of carbon, the 
index of which is 1-678, being, I believe, the highest of any known fluid.” 
The Mode in tuhich Bacteria Midtiply. — Herr Grimm, in the “ Archiv fiir 
mikrosc. Anatomie,” describes the reproduction of Bacteria and Vibriones 
from his own investigations. He has observed their conjugation and flssi- 
parous multiplication, and also has seen leucocytes breaking up into granular 
matter, which ultimately assumed the form of Bacteria. 
Irish Support to Microscopy. — The Boyal Irish Academy has given the 
sum of 40^. to Mr. G. H. Kinahan, in order that he may continue his 
valuable researches into the microscopical structure of rocks, a subject on 
which for some time Mr. Kinahan has been engaged. 
Mode of Observing Tissues in the Living State. — This subject, which is of 
the utmost importance at the present moment, was dilated on as follows by 
Mr. Schafer, at one of the meetings of the Medical Microscopical Society. 
The report says that Mr. Schafer, having dwelt briefly on the importance 
of the subject, remarked that the investigation of a subject was not complete 
till it had been microscopically studied in the living state, and that such 
examination, at least for warm-blooded animals, should be carried on at the 
temperature of the body. Much was to be learnt from the investigation of 
tissues still attached to the living body, for thus had cell migration been 
discovered by Cohnheim in the frog’s mesentery, and experiments on em- 
bolism had been made in that animal’s tongue ; while the tail of the tadpole 
had taught us much about connective-tissue corpuscles, and the development 
of blood-vessels. Muscular tissue was best seen in the living state, in the 
smaller crustaceae. Living tissues, removed from the body, allowed of being 
studied in many ways: some immediately without any addition whatever, 
as red blood coi-puscles, and striated muscular flbre ,* while if any addition 
were necessary, a saline solution of 0-75 per cent., or serum would be best. 
For some purposes a moist chamber might be necessary, such as Becklinghau- 
sen’s, in which frogs’ blood had been preserved for days in a living condition 
(Schultze’s “Arch.” 1866). Another form was Strieker’s putty stage, which 
was also useful for the application of electricity in microscopical research by 
means of two electrodes of tin-foil, the points of which nearly meet in the 
centre of the stage. Mr. Schafer Anally described and exhibited various forms 
of warm stages, one kind of which, as Schultze’s, was heated by means of a 
lamp applied to metal arms, which conducted the heat to the object-bearers ; 
another kind, as Strieker’s, in which a constant temperature was maintained 
by means of a current of warm water kept continually flowing through it ; 
while another very ingenious form of stage, somewhat similar to Strieker’s, 
