108 The American Naturalist. [February, 
as compounds of proteid substances with nucleic acid, the 
various members of the group differing in the proportion of 
proteid matter to this phosphorus-rich acid. Thus, we may 
have a chain of nucleins, one end of the series being repre- 
sented by nucleic acid itself with its 9 to 11 per cent. of phos- 
phorus and without any admixed proteid, such for example as 
is found in the heads of the spermotozoa, which are doubtless 
derived from the nuclei of the spermatogenic cells; while in 
the middle of the series are the nucleins proper consisting of 
proteid with varying amounts of nucleic acid, and at the other 
extreme nucleins composed almost entirely of proteid, con- 
taining at the most only 0.5 to 1.0 per cent. of phosphorus and 
represented by the substances generally known as nucleo- 
albumins. 
Nucleins are not digestible in artificial gastric juice, while 4 
nucleo-albumin, as already stated, undergoes a partial diges- 
tion, the excess of combined proteid matter being converted 
into soluble products, while a typical nuclein remains as an 
insoluble residue, which however may be dissolved by weak 
alkalies. With this understanding of the general character of 
of the nucleins, many of the micro-chemical observations 
recorded by different workers in cytology become intelligi- 
ble. Take as an illustration the work of Zacharias’ on ves® 
table cells. This observer, as you remember, made a large 
number of digestive experiments with artificial gastric juice, 
and noted the occurrence in the nucleus of two distinct sub- 
stances indigestible in pepsin-acid solution, which differed 
from each other in their solubility in acids and alkalies. As 
a result, Zacharias states that the resting cell nucleus consists 
of a ground mass composed in great part of nuclein, while the 
nucleoli consist of albumin and plastin. Remove the albu- 
min from the nucleus by digestion, and the nuclein will dis- 
solve in dilute alkali, leaving a network of plastin. Further, 
Zacharias states that plastin is an essential constituent of the 
total protoplasmic content of the cell, including the nucleus 
and the chromatophore. Now, note the differences between 
the nuclein and the plastin as defined by Zacharias. Plastid, 
*Botanische Zeitung. 45th Jahrgang, pp. 281 and 329. 
