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brought into play to determine the growth of a tissue from an 
amorphous blastema, and, moreover, to give the elements of 
that tissue peculiar and characteristic properties; and, lastly, 
we have to inquire how various tissues combine to form organs. 
Each of these problems requires for its solution a greater 
amount of chemical and physico-physiological knowledge than 
we yet possess. 
The researches of Turpin and Dumortier, Schleiden, 
Schwann, Henle, Valentin, Reichert, and others, have thrown 
considerable light on the manner of growth of tissues, and no 
reasonable doubt can be now entertained that the Cell-theory, 
as elaborated by these and other observers, and specially ap- 
plied to the development of animal structures by Schwann, 
fully and satisfactorily explains the mode of formation and de- 
velopment of several tissues and organs. Notwithstanding, 
however, the reception of this theory, even in its extreme and 
exclusive application, as insisted on by Schwann, in most schools, 
soon after its promulgation, it has been found defective in many 
points, and has been and is still questioned by several observers 
of authority. Having devoted much attention to this subject, 
I have become conyinced by repeated observations that there 
are several tissues which at no period of their development 
exhibit any evidence of formation by cells, and consequently 
that cells cannot be considered as the only plastic germs or 
formative elements of organic life. 
The following researches and observations appear tome to 
support the opinion now stated. 
As the common hen’s egg offers great facilities for the study 
of the formation of structures, I have made some careful ob- 
servations of the microscopic elements, which it presents both 
before incubation and at certain periods after the commence- 
ment of that process. 
1. A portion taken from the mass of the yolk, and sub- 
mitted to a power of 420 D., exhibited the following elements : 
a. Anabundance of minute granules, covering the greater 
part of the field, ofa light-yellowish colour, with a dark border 
