271 
Protoplasm by Aid of Microdissection. 
or non-existence of a plasma-membrane. To one concerned in establishing 
the possible morphological identity of a protoplasmic membrane there is but 
one course, namely, accurately to describe the thing and let this description 
stand as a definition for the name used. 
Material. 
The data upon which the following discussions are based were obtained 
by the study of a considerable variety of material. While the conclusions 
reached may be regarded as pretty generally applicable, it is to be under- 
stood that the statements made refer only to the organism under discussion 
at the time. Some of the physical properties of protoplasm are character- 
istic of all protoplasm, yet prominent dissimilarities do occur between even 
closely related species. 
The following types are the chief ones used for this study : the 
myxomycetes Ceratiomyxa, Badhamia, Arcyria, Cribraria, and Fuligo ; the 
ova of the rock-weed Fucus ; the freshwater algae Spirogyra and Vaucheria ; 
Elodea ; the bread-moulds Rhizopus and Zygorhynchus ; pollen tubes of 
the Blue Flag Iris versicolor , of the Beach-pea Lathyrus maritimus , and of 
the Dog’s-tooth Violet Erythronium revolutum\ the protozoa Amoeba and 
Euplotes ; the ova of the sand-dollar Echinarachnius , of the sea-urchin 
Tripneustes esculentus , and of the silver (English) hake Merluccius . 
The experimental work on these forms was done mostly in the 
Botanical Laboratory of the Johns Hopkins University. The work on 
marine forms, however, was carried on at the Harpswell Laboratory, South 
Harpswell, Me., and at Ocho Rios, Jamaica, B.W.I. 2 
I. PROTOPLASMIC MEMBRANES. 
No topic in biophysics probably has been the subject of so much con- 
troversy as that of the plasma-membrane and its bearing on the phenomenon 
of permeability. Opinions upon it differ so widely that while its very 
existence is questioned by some workers, others positively assert that an 
actual morphologically and physiologically definite surface layer can be 
clearly demonstrated. Thus de Vries ardently supports its existence as 
a morphological entity, while Kite (23, p. 298) views it as a ‘ hypothetical ’ 
structure, and Fischer (15, p. 225) calls it a e figment of the imagination ’. 
There are three main lines of attack on this problem, no one of which 
can by itself give conclusive evidence, although a combination of the 
1 Other difficulties in nomenclature, especially in reference to such common colloid chemical 
expressions as ‘ gel 1 coagulum ’, &c., are considered in the paper dealing with other physical 
properties of protoplasm already referred to (38). 
2 I am indebted to Director J. S. Kingsley for the use of a room at the Harpswell Laboratory. 
To Frank Cundall, Esq., I am greatly obliged for his kindness in placing the facilities of the Institute 
of Jamaica at my disposal. 
