76 STUDIES ON PATHOLOGIC OVA. 



impossible to recognize the true nature of a small nodule upon gross inspection 

 alone, it is often impossible to make a correct classification except by careful 

 microscopic examination of the stained sections. Consequently, some of these 

 doubtful specimens are bound to get into the wrong category, for they must be 

 classified when received, and largely upon the basis of inspection by the unaided 

 eye and slight magnification with the hand-lens or the binocular microscope. 

 Hence, it was later found that 13 of the specimens placed in this group do not 

 belong here. None of these 13 specimens contained a cyema, and in the case of 

 2 others a decision was impossible, even upon microscopic examination of stained 

 sections of the specimens. 



Although some of these small nodular cyemata measure but a few millimeters 

 in length, they nevertheless should show considerable differentiation had they 

 undergone normal development. This, however, is not the case, for some of them 

 are composed simply of undifferentiated mesenchyme, with or without a cavity, 

 and a slightly differentiated outer layer. None of them have even approximated 

 the differentiation of a normal specimen of the same size, wholly regardless of 

 age. In certain cases the rudiments of some of the organs can be recognized, but 

 others have undergone partial or complete dissociation, making recognition of 

 individual organs impossible. Usually a somewhat undifferentiated portion can 

 be recognized as belonging to the central nervous sustem ; the crelom is frequently 

 indicated, and some myotomes; liver and heart tissue can be detected. Neverthe- 

 less, most of them are small sessile nodules showing little differentiation. In some 

 instances these nodules are composed of one kind of tissue only, usually mesen- 

 chyme, wholly uncovered by what could be spoken of as either ectoderm or epider- 

 mis. In others, however, epidermis is present, and the specimens containing heart 

 and liver tissues are those which border upon the next group. 



Although 4 or 5 mm. long, these nodules generally show less differentiation 

 than a normal specimen of the length of 2 or 2.5 mm. As is well known since the 

 description of a 4.5 mm. embryo by His, specimens of this length should show 

 considerable development of the central nervous system with differentiation into 

 its various main divisions. The eye and ear should have begun to form, and the 

 maxillary and mandibular processes should be present. The dorsal segmentation 

 also should be very evident, and the differentiation of the circulatory, urogenital, 

 and digestive systems should be considerable. That the cyemata in the nodular 

 group fall behind the stage of development reached by normal specimens of corre- 

 sponding length quickly becomes evident, even upon cursory examination. Not 

 rarely the amnion upon which these small nodules are sessile has become de- 

 tached from the chorion. In two cases the latter was absent altogether, but its 

 absence must undoubtedly be attributed to mechanical causes. 



The histologic condition of some of these small specimens is well characterized 

 by the term "dissociation," introduced by Mall. Phisalix (1890) also spoke of 

 the tissues of some of the embryos being "desagregre." As I understand this 

 term, it refers to the disorderly mingling of the tissues which belong to different 

 organs, so that the outlines of these organs no longer can be distinguished. This 



