86 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Nucleus of Diatoms.* * * § — Dr. P. Miquel asserts that, notwithstanding 
the siliceous envelope by which most diatoms are protected, they are 
peculiarly liable to destruction by Infusoria and by unfavourable vital 
conditions. It is only their extraordinary numbers, and the rapidity 
with which they multiply, that preserves them from extermination. The 
Infusoria may even carry on a parasitic existence within the cell. The 
diatom-cell consists of four parts ; the external gelatinous layer or coleo- 
derm, often erroneously called the thallus, the siliceous coat, the proto- 
plasm, containing phseoleucites, oil-drops, and other substances, and the 
nucleus. As a rule, the protoplasm completely fills up the space within 
the valves ; this is especially well seen when the microfrustules are 
transforming themselves into auxospores or megafrustules. 
The nucleus of diatoms is often exceedingly difficult to distinguish,, 
in consequence of its being masked by the phasoleucites, or because its 
index of refraction differs only very slightly from that of the surrounding 
protoplasm. A favourable species is Coscinodiscus concinnus. By the use 
of suitable reagents,! the author was able to demonstrate the existence 
of a nucleus in a large number of species of diatom, even in some very 
minute ones, and he asserts that cell-division is always preceded by divi- 
sion of the nucleus ; the protoplasm then divides into two nearly equal 
parts, each carrying with it one half of the bands of endochrome ; there 
is no sudden formation of a siliceous septum. 
> Spores of Diatoms.! — Replying to the arguments of Dr. Miquel, 
l’Abbe Comte F. Castracane adduces further evidence in favour of his 
view that the most common mode of propagation of diatoms is by means 
of endogenous spores. 
Schmidt’s Atlas der Diatomaceen-kunde. — The latest part pub- 
lished of this magnificent work is a double one, Hefte 18, 49, pis. 189-96. 
It is entirely occupied by recent and fossil forms of the genus Cocconeis, 
including a few that have been referred to Rcvplioneis, 
/3. Schizomycetes. 
Present Condition of the Immunity Question^ — In a review of the 
present condition of the question of immunity, M. E. Metschnikoff remarks 
that the humoralists have shifted their ground. Thus Buchner now 
attributes the bactericidal power to leucocytic products, and R. Pfeiffer 
assumes that immunity is due to liquids secreted by endothelial cells, 
while Behring supposes that, besides passive immunity due to the body- 
juices, there is an active immunity due to cell-function. In passive 
immunity, set up by serum vaccine or other preventive substances, the 
author only sees an increase in cell reaction ; while even the antitoxic 
action of humours is also to be ascribed to cell defence, and not to 
destruction of the toxines. 
Facts are quoted to show that the view that bacteria are destroyed by 
secretions from eosinophilous leucocytes is untenable, while the theory of 
phagocytosis has constantly received support ever since it was promul- 
* Le Diatomiste, ii. (1894) pp. 105-118 (1 pi.). t Of. infra , p. 127. 
j Atti Accad. Pontif. Nuovi Lincei, xlvii. (1894) pp. 48-52 ; Le Diatomiste, ii. 
(1894) pp. 118-22. Cf. this Journal, 1894, p. 239. 
§ Ann. Inst. Pasteur, viii. (1894) pp. 706-21. 
