OCCURRENCE OP LOCALIZED ANOMALIES. 201 



In my paper on monsters I stated that on account of faulty implantation of 

 the chorion the nutrition of the embryo is affected, so that if the ovum is very 

 young the entire embryo is soon destroyed, leaving only the umbilical vesicle 

 within the chorion; this also soon disintegrates, and the chorionic membrane in 

 turn collapses, breaks down, and finally disappears entirely. In older specimens, 

 on the other hand, the process of destruction takes place more slowly, and thus 

 we many account for a succession of phenomena which correspond to the seven 

 groups of pathological ova referred to above. 



Kellicott, in his discussion of monsters, dropped the subject by stating that 

 the embryo is a monster simply because it is disorganized. In my original study 

 I really went, I believe, a step farther than Kellicott, for I attempted to analyze 

 the process of disorganization more thoroughly and demonstrated that in the 

 beginning it is accompanied by cytolysis, but as it progresses more rapidly it 

 results in histolysis, and that these two processes do not act with equal severity 

 on all parts of the embryo. When we consider the ovum as whole, it is the embryo 

 itself which is first destroyed, while within the embryo the central nervous system 

 or the heart is the structure first affected. Morphologically, these changes are 

 accompanied by a destruction of certain cells and tissues, leaving other portions 

 which continue to grow in an irregular manner. For this reason I speak of the 

 tissues which are first affected as being more susceptible than the others. The 

 entire process of disorganization, resulting in an irregular product, I have termed 

 dissociation. In a general way this explanation is accepted by Werber (1915, 

 1916), but he employs the term blastolysis instead. 



At the time I prepared my paper on monsters, Harrison was just beginning 

 his interesting experiments in tissue culture in our laboratory. Since then this 

 method of study has given us clearer insight into the independent growth of tissues. 

 I was fully convinced from the study of pathological embryos that tissues con- 

 tinue to grow in an irregular manner, thus arresting normal development; but since 

 we are more familiar with the growth of tissues, as revealed by Harrison's method, 

 we can understand a little better the process of dissociation. In fact, we have in 

 our collection two striking examples of tissue culture in human embryos. In one 

 the cells had formed an irregular mass which was growing actively, but the contour 

 of the organs had been entirely lost. In the other, from a tubal pregnancy, for 

 some unknown reason the ovum had been completely broken into two parts, 

 which in turn had cracked the embryo, and from each piece there had been a 

 vigorous independent tissue growth, or, as we may now say, a tissue culture. Accord- 

 ingly, when an embryo is profoundly affected by changed environment the develop- 

 ment of one part of the body may be arrested, while the remaining portion may 

 continue to grow and develop in an irregular manner. In very young embryos, 

 tissues or even entire organs become disintegrated, as can be easily recognized 

 by the cytolysis and histolysis present, and the resultant disorganized tissue can 

 not continue to produce the normal form of an embryo. If this process is sharply 

 localized, for instance, in a portion of the spinal cord or in the brain, spina bifida 



