284 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Those that have been reading Prof. Kirsch’s paper on cytology have 
learned that the nucleus, while it appears to be formed of a reticulation 
or network, is in reality composed of a single fine tubule much con- 
voluted upon itself, the apparent network being produced by the crossing 
of the tubule over its preceding convolutions. The nucleus is in struc- 
ture only a single, very much twisted tube, whose hollow is filled with 
a substance that has been named the nuclein. In the intestinal cells of 
Oniscus beautiful optical sections of this are obtainable, since the nuclein 
takes the stain with great avidity. The network is here conspicuous, and 
the meshes, unlike those of the protoplasm of the cell, are fine and small. 
Altogether, therefore, the intestinal cells of this common animal cannot 
be excelled as objects in which to examine the structure of the proto- 
plasm— a subject that is always interesting, and should be seen and 
understood by every microscopist.” 
Methods of Technique in Embryology of Frogs.* — Mr. T. H. Morgan 
describes his methods as follows : — “ The eggs, during the periods in which 
it is difficult or impossible to remove the inner jelly membrane, can be 
freed in the following manner. With a pair of sharp scissors each egg must 
be cut out from the general jelly-mass, retaining as small an amount of 
surrounding jelly as possible. It is then put into an alcoholic solution 
of picric acid for an hour or longer (one to twelve). The solution is 
prepared by saturating 35 per cent, alcohol with picric acid, and adding 
the same amount of sulphuric as in Kleinenberg’s solution. The solu- 
tion is not diluted, but used saturated with picric acid. The eggs are 
then washed for several hours in 35 per cent, alcohol, several hours in 
50 per cent, alcohol, and placed in 70 per cent, for several days, changing 
the alcohol once or twice if necessary. About the second day the inner 
membrane begins to swell, due to a slow osmotic action, I think, as the 
membrane is stretched by tension from within. On the third or fourth 
day the swollen membrane may be pierced by a sharp needle, and the 
egg taken out, which is then placed permanently in 80 per cent, alcohol. 
The method is exceedingly simple, and consists largely in waiting a few 
days for the osmotic action to take place. Such eggs, if properly 
prepared, are in excellent histological condition. This simple method 
has proved so successful that I have not further experimented with it. 
It is possible that it may be improved by varying the strength of alcohol 
used, but I have not seen the need of looking further. The membrane 
does not swell in stronger alcohol than 70 per cent., and weaker would 
macerate the eggs. 
Certain precautions are necessary in imbedding the eggs to prevent 
brittleness. This is obviated by soaking the eggs before imbedding, 
for several hours, in a solution of turpentine saturated with paraffin, 
and kept in a warm place — not so hot as the water-bath (50° C.). 
Heat causes the egg to become brittle. This is obviated by the 
above process of soaking, so that the egg need not remain so long as 
an hour in the melted paraffin of the water-bath. 
In the younger stages there is no need for very thin sections, but 
sections 10 yu. thick are sufficient for all purposes. If the sections 
are cut too thin the yolk tends to break up and crumble.” 
* Amer. Nat., xxv. (1891) pp. 759-GO. 
