Marcu 29, 1901.] 
histology these two subjects are generally 
neglected or at most appear only as matters 
of incidental reference. The force of tradi- 
tion makes us apply these terms as if they 
correspond exclusively to pathological con- 
ditions. This tradition might still prescribe 
our mental attitude, were it not that the 
studies of the last dozen years have made 
us familiar with the enormous extent, va- 
riety and rapidity of the destructive degen- 
erations which go on in the pregnant uterus 
of placental mammals, a degeneration which 
takes place without affording a trace or a 
suggestion of any pathological modification 
whatsoever of the organ. To our inherited 
prejudices the uterine phenomena alluded 
to are startling, but their evidence before 
the tribunal of biology has settled the case 
in favor of the plea that hypertrophic de- 
generation is a normal factor in typical 
healthy development. 
The normal and pathological changes as- 
sociated with the death of cells, and conse- 
quently also of the tissues which are formed 
by cells, are so nearly identical that they 
may be combined in a single discussion. 
For the more convenient presentation of 
the subject the following table has been 
prepared. Concerning the table little ex- 
planation is necessary. 
A few special points need mention. The 
distinction made between necrobiosis and 
degeneration corresponds to recognizable 
differences, but our present knowledge is 
insufficient to provide clear definitions for 
the two closely related types of indirect 
cell death. I feel much doubt as to the 
propriety of including atrophy in the table 
at all, since it seems to me that we ought, 
perhaps, not to regard atrophy as a phe- 
nomenon of a distinct class, but merely as 
a result of necrobiotic or degenerative al- 
terations in cells and organs. Under the 
heading ‘degeneration’ the division into 
‘cytoplasmic’ and ‘paraplasmic’ takes us 
beyond our present knowledge, while the 
SCIENCE. 
491 
division ‘ nuclear’ is added rather to satisfy 
a biological conscience than to represent a 
part of our knowledge. 
Death of Cells. 
First—Causes of death. 
a. External to the organism. 
1. Physical (mechanical, chemical, ther- 
mal, etc. ). 
2. Parasites. 
b. Changes in intercellular substances (prob- 
ably primarily due to cells). 
1. Hypertrophy. 
2. Induration. 
3. Calcification. 
4. Amyloid degeneration. 
ce. Changes inherent in cells. 
Second—Morphological changes of dying cells. 
a. Direct death of cells. 
1. Atrophy. 
2. Disintegration and resorption. 
b. Indirect death of cells. 
1. Necrobiosis (structural change pre- 
cedes final death). 
2. Hypertrophic degeneration (growth 
and structural change often with 
nuclear proliferation precede final 
death). 
Third—Removal of cells. 
a. By mechanical means (sloughing or shed- 
ding). 
b. By chemical means (solution). 
ce. By phagocytes. 
The preceding table represents the only 
attempt of the kind known to me, and like 
other first attempts is undoubtedly very 
imperfect. It embodies obviously no new 
facts. But, because it is frequently a scien- 
tific gain to systematize our information, I 
hope the table may be useful, and it will 
certainly serve its immediate purpose, 
namely, to guide our discussion of the nor- 
mal changes which follow after cellular 
differentiation. 
As the time at our command is brief let 
us pass by the consideration of the causes 
of cell death. I will remark only that I 
think amyloid degeneration may be found to 
occur in the placental decidua of the human 
pregnant uterus and perhaps in other nor- 
mal structures. No positive information 
