2 93 
Protoplasm by Aid of Microdissection. 
hold its own against disorganization is the following observed behaviour of 
the escaped protoplasm of a sea-urchin ovum. I have watched such free 
protoplasm go through the process of rounding up, which is, when the 
protoplasm is very viscous, comparatively slow. Usually the process of 
healing is completed and the escaped droplet of protoplasm maintains its 
identity. Often, however, the droplet is not quite fully formed, part of its 
surface remaining momentarily ragged. This exposed, ragged protoplasm, 
without any apparent membrane, remains, until the turning-point in the 
process is reached, quite immiscible in the water with which it is in contact. 
One can almost imagine the protoplasm ‘ struggling ’ to retain itself. If it 
succeeds, the droplet is formed. If it fails, miscibility results, as a conse- 
quence of disorganization. 
To deny the water-miscibility of a hydrosol forces one to explain an 
apparent incongruity. But one must bear in mind that protoplasm is not 
a simple emulsion of two phases such as milk, but is exceedingly complex, 
possessing an intricate colloidal structure and a still more intricate and 
as yet unfathomable organization. 
MacDougal ( 25 , p. 601) has suggested that solubility of protoplasm 
may depend c upon differences in the carbohydrate component ’, i. e. 
‘ living matter in which the pentosan was a mucilage like gum arabic would 
be miscible with water, while a pentosan like tragacanth would be less 
soluble, and a group like agar, for example, would not appear to be soluble 
at all’. Solubility ‘might also result from the character of the amino- 
compounds or proteins present, especially in a protoplasm rich in nitrogen ’. 
This does not, it seems to me, explain the true state of affairs. It is 
probably structure primarily which keeps protoplasm from losing its 
identity as living substance by mixing in the surrounding water. I do not 
mean to imply that structure alone is the deciding factor, for chemical 
changes may conceivably play at least a minor part. For example, oil, 
through the activity of an enzyme, may be split into glycerine and an acid 
and thus become soluble in water. But the emphasis in the case of proto- 
plasm should, I think, be placed upon structure rather than upon chemical 
composition. 1 
Gaidukov ( 16 , p. 161) says that ‘ protoplasm can only be a hydrosol if 
it is covered by a protective wall (plasma-membrane) ’. It is. I grant, 
difficult to conceive of a hydrosol being immiscible in water unless a mem- 
brane intervenes. That a membrane does usually intervene is true, but it is 
itself protoplasm and as such gives no evidence, even when liquid, of 
miscibility. The membrane is apparently not the cause but a result of 
1 It is possible that the large size of the molecules of the components of protoplasm is a factor 
in preventing miscibility. The diffusion rate of a solute varies directly as the molecular energy (or 
the absolute temperature) and inversely as the viscosity of the liquid and dimensions of the particles 
(28, p. 105). The protein molecules which make up a large part of protoplasm are among the 
largest known, consequently they diffuse very slowly. 
