494 
plain the extraordinarily rapid disappear- 
ance of the degenerated material in the 
obplacenta the only available hypothesis 
seems to be that of a chemical change by 
which the material becomes soluble or is 
dissolved, for we see the disappearance of 
the substance taking place in the very 
heart of the layer, and not merely at the 
surface. Sloughing is impossible and there 
are no phagocytes, leaving the chemical 
explanation as the only one I have been 
able to conceive. The contemplation of the 
described phenomena of the rabbit’s obpla- 
centa inevitably raises the question—do we 
not tend in our explanations of the removal 
of necrosed and degenerated tissues to at- 
tribute too much to phagocytes and too 
little to direct chemical action? May it 
not be that the body produces histolytic 
toxins, which can destroy tissues somewhat 
as do snake-poisons ? 
The cycle of changes through which cells 
pass is obviously longer than the period of 
development and the differentiation, yet its 
phases all belong together as members of a 
single series. We lack a word to designate 
the entire series of changes, and for the lack 
of such a word often fail to appreciate the 
essential unity of progressive and regressive 
modification of cell-structure. Accordingly, 
I wish to propose the new term cytomorphosis 
to designate comprehensively all the struc- 
tural alterations which cells, or successive 
generations of cells, may undergo-from the 
earliest undifferentiated stage to their final 
destruction. 
PART II. PATHOLOGICAL DIFFERENTIATION. 
We have now completed our brief re- 
views of the four fundamental successive 
stages of cytomorphosis. These stages 
are : 
First .Undifferentiated. 
Second. Progressive differentiation, which 
itself often comprises many successive 
stages. 
SCIENCE. 
[N. S. Vou. XIII. No. 326. 
Third. Regression (necrobiosis or de- 
generation). 
Fourth. Removal of the dead material. 
Let us now apply some of the concep- 
tions won to the interpretation of patho- 
logical differentiation, remembering all the 
time that the interpretation of disease is a 
distinct and different problem. Although 
presumably pathological differentiation is 
the sole and exclusive cause of disease and 
no disease arises from any other immediate 
cause, yet the disease must be regarded as 
the result and, owing to the physiological 
correlation of the organs, this result may 
include many secondary effects, some of 
which are often of the greatest diagnostic 
' value, and therefore likely to divert atten- 
tion from the primary structural cause. 
Our review of normal conditions fur- 
nishes us with three general conceptions, 
which are valuable for their pathological 
applications,—namely : 
First. That each germ layer has a spe- 
cific and exclusive share in the production 
of tissues. 
Second. That undifferentiated cells, char- 
acterized by having only a small amount of 
unspecialized protoplasm, exist not only in 
the embryo, but also throughout life in cer- 
tain parts of all three germ-layers. 
Third. That differentiated cells character- 
ized by having a larger amount of special- 
ized protoplasm, form most of the organs of 
the adult and are incapable of undergoing 
any new unlike differentiation, though they 
are still capable of completing their ecyto- 
morphosis, by necrobiosis or degeneration. 
We must apply these conceptions, accord- 
ing to my belief, as rigidly to pathological 
as to normal development. Thus, as to the 
germ-layers, it ought to be possible even 
with our present knowledge, to show their 
pathogenetic values, so that every elemen- 
tary student as a matter of course can be 
taught to classify accurately most patho- 
logical differentiations, and to accept such 
