66 SUMMARY OF CURRENT RESEARCHES RELATING TO 
but lie between them, and form terminal expansions on their surfaces. 
It may be said that the long villi are mainly, though not exclusively, the 
bearers of the terminal nervous expansions. They serve to increase the 
superficial extent of the essential electromotor tissue. 
Hard Tissues of Vertebrates.* — Dr. C. Rose has a very learned 
article on the different forms of hard tissues, which he classifies as 
follows : — 
A. True hard tissues (arising from odontoblasts and osteoblasts). 
(1) True ivory, dentine or orthodentine (including normal 
dentine, vitrodentine, and vasodentine). 
(2) Trabecular dentine. 
(3) Osteoid tissue. 
(4) Bone. 
(5) Osteodentine. 
B. Calcified connective tissue. 
Unlike any of the above, whose origin is from connective tissue, 
enamel is formed from epithelial cells. It is of much wider occurrence 
than used to be supposed. In the much discussed case of the dogfish, 
the epithelial sheath forms an enamel cuticle— a superficial protective 
mantle — which may be regarded as the first stage in the formation of a 
true enamel. 
c. General. 
The Living Substance. j — Mrs. G. F. Andrews has made a study of 
protoplasm, and gives an account of its visible structure, its inclusions, 
its areal differentiations, its activities, &c., working gradually up to 
reproduction, heredity, habit, and instincts. She sums up her own 
observations, several of which have been previously referred to in this 
Journal, and insists on the idea of “an infinitely graded series of vesicu- 
lations of the protoplasmic foam.” “ Protoplasm is a very complex 
emulsion, having the physical arrangement of a very finely subdivided 
variably viscid foam, which characters are coextensive with the con- 
tinuous element of all visible optical reticula.” Unless we misunderstand, 
the book is not so much a treatise on protoplasmic phenomena as an 
expression of a certain interpretation which is summed up thus : “ The 
facts seem to warrant present belief that the living substance of all 
organisms is one physiologically continuous living plasma, homogeneous 
throughout in its intrinsic powers and properties, but having vailed local 
and temporary habits of self-expression, which are largely and inextri- 
cably correlated with physical and chemical conditionings of its form 
and composition as complex emulsive foam — yet not to be wholly 
identified with, nor wholly explained by these.” 
Theory of the Functions in Living Matter.t — Miss F. A. Welby 
has done good service in translating Prof. E. Hering’s article (1888) on 
the theory of the functions in living matter, in which he expounded his 
conception of metabolism as consisting of two closely interwoven pro- 
cesses of assimilation and dissimilation. 
* Anat. Anzeig., xiv. (1897) pp. 21-31, 33-69 (28 figs.), 
f ‘ The Living Substance as such and as Organism,’ Boston, 1897, 8vo, 176 pp. 
x ‘ Brain,’ 1897, pp. 232-58. 
