32 MALL. [Vor. XIX. 
placental parasite. Of course, a “rescue” like this is out of 
the question in nearly all cases, and the life of the embryo is 
of short duration after its heart has ceased to beat. 
Specimens similar to Bardeen’s and mine have often been 
found in chicks by Dareste and by Panum. Panum describes 
quite extensively the changes which take place in chick mon- 
sters. He recognizes in his classification that flattened mon- 
sters are of two kinds: (1) Anzmic ones, in which no blood 
is found, and (2) those in which red blood had been found 
but most of the vessels are retained in the area vasculosa. In 
these probably the vascular anlage was destroyed very early 
or it began in the area vasculosa and did not develop into 
the embryo. The result is similar to that obtained by Bar- 
deen, Knower and myself. 
It is clear, I hope, that certain parts of the embryo are more 
susceptible to insults than others, and this must be admitted in 
order to explain why potassium stops the heart, lithium affects 
in a peculiar way the movement of the protoplasm in the 
blastomeres, and sodium produces spina bifida by arresting 
the movements which close the spinal canal. In order to 
analyze the situation we must concern ourselves mostly with 
simple reactions in their early stages, for they are not under 
way long before they become very complex and beyond 
our reach. Mesenchyme is less susceptible than nerve tissue, 
and the brain is more susceptible than the spinal cord; and 
so on. A susceptible tissue when affected undergoes certain 
morphological changes well recognized by Panum. Panum 
pictured to himself a kind of inflammation of the tissues, 
parenchymatous, due to disturbances in the nutrition of the 
part, but it is by no means clear that anything like inflamma- 
tion in the healing of wounds takes place in embryos or in 
the various tissues after they have become partly necrotic. 
Often it is noticed that cells accumulate in portions of the 
embryo, and His thought that they wandered out from the 
blood-vessels. In my former publications I spoke of these 
cells as the wandering cells of His. Hertwig and Bardeen 
speak of necrosis, and there is every evidence that destructive 
