42 
under a 1.5 mm. immersion objective— 
which is, of course, a perfectly arbitrary and 
- artificial limit? It is impossible to doubt 
that powers still higher than any at our 
command would reveal the existence of 
granules still smaller, and that what ap- 
pears as ‘continuous’ or ‘homogeneous’ 
substance is itself an emulsion beyond the 
range of vision. 
We may now inquire whether the coarser 
visible alveolar structure is characteristic 
of all protoplasm. This question has in a 
measure already been answered, for in these 
very eggs we have seen the alveolar struc- 
ture giving rise to a fibrillar one in the 
aster-formation—-in other words, the proto- 
plasm of the same cell may in different 
phases pass back and forth from one state 
into another. This fact appears in its clear- 
est form when we study the growth of the 
ovarian ova, which gives us many addi- 
tional suggestions of high interest. The 
entire coarser alveolar structure, as described 
above—i. e., the foam structure of Biitschli—is in 
these eggs of secondary origin. The very young 
living ovarian eggs consist of ‘homoge- 
neous’ protoplasm, such as has been de- 
scribed by many botanists in the embryonic 
tissue-cells, through which are irregularly 
scattered a few small spheres and many ex- 
cessively small granules. As growth pro- 
ceeds both the spheres and the granules in- 
crease in size, the latter enlarging to form 
new spheres, while new granules continu- 
ally emerge from the protoplasmic back- 
ground into the limits of vision. In the 
middle stages of growth the protoplasm is 
thus converted into an emulsion, being 
filled with spheres of all sizes, ranging 
downwards from 1.0 micron to the smallest 
granules, but still showing no regular ar- 
rangement (Fig. 1, d). As the egg ap- 
proaches maturity the spheres become dif- 
ferentiated into two groups, the larger 
ones becoming approximately of the same 
size, to form the alveolar spheres and 
SCIENCE. 
[N.S. Vor. X. No. 237 
crowding together, while the smaller ones 
remain as the microsomes and finer gran- 
ules embedded in the remains of the con- 
tinuous substance which forms the basis of 
the meshwork. In one sense, therefore, the 
alveolar spheres and the microsomes are 
only different stages in the same morpho- 
logical series—though it should be remem- 
bered that they differ chemically as well as 
in size, and I donot mean to imply that the 
one may develop inte the other—and both 
the alveolar and the fibrillar or reticular 
structures in these eggs are of secondary 
origin. If this be the case neither of 
these types of structure can be of funda- 
mental importance; and I fully agree with 
the opinion of Kolliker, which has been 
adopted by an increasing number of later 
observers, that no universal or even general 
formula for protoplasmic structure can be given. 
The evidence indicates that alveolar, gran- 
ular, fibrillar and reticular structures are 
all of secondary origin and importance, and 
that the ultimate background of protoplasmic 
activity is the sensibly homogeneous matrix or 
continuous substance in which those structures 
appear. 
I do not mean to say that this is the 
only ‘living’ element in the cell. The dis- 
tinction between ‘ living’ and ‘lifeless,’ be- 
tween ‘protoplasmic’ and ‘ metaplasmic,’ 
substances is exceedingly difficult to define 
—largely on account of our vague and in- 
‘consistent use of terms, for in practice we 
continually use the word ‘ living’ to denote 
various degrees of the vital activity. Proto- 
plasm deprived of nuclear matter has lost, 
wholly or in part, one of the most char- 
acteristic vital properties, namely, the 
power of synthetic metabolism ; yet we still 
speak of it as ‘living,’ because it may for a 
long time perform some of the other func- 
tions, manifesting irritability and con- 
tractility, and showing also definite coordi- 
nations of movements (asin the enucleated 
protozoan) ; and, in like manner, various. 
