104 CARNEGIE INSTITUTION OF WASHINGTON. 



osmotic effects of the injected hypotonic and hypertonic solutions. 

 Any future studies on the determination of the brain volume will have 

 to take these factors into consideration. 



Dr. Weed has extended his earlier observations, and those of Dr. 

 Essick, on changes in the cells of the arachnoidal membrane of the 

 brain, and finds that the change in morphology of these cells, when ob- 

 served in full-grown and old cats, first shows itself as a localized pro- 

 liferative process. Ordinarily, these cells form dense, nodular swellings 

 well differentiated from the adjacent unchanged arachnoid membrane, 

 which, after attaining a definite size, undergo either degeneration and 

 calcification or more outspoken proliferation, resulting in so-called 

 endotheliomata. In some animals, however, the proliferative pro- 

 cess extends diffusely over the membrane. The evidence thus far in- 

 dicates that the morphology of the covering cells of the arachnoidea 

 depends not only on the physiological state of the membrane, but also 

 upon the age of the particular animal. The complete report of this 

 work is now in preparation. 



PATHOLOGICAL STUDIES. 



An interesting, very young human ovum has been studied by Pro- 

 fessor J. Whitridge Williams. This specimen is unique in the fact 

 that it gives us information concerning the mechanism of the process of 

 abortion, the abortion being actually in progress at the time of the re- 

 moval of the uterus. One pole of the decidua capsularis had ruptured 

 and the corresponding pole of the ovum was extruded through the de- 

 fect; the opposite pole of the ovum still retained its organic connection 

 with the adjacent decidua by means of villi, which were in an advanced 

 stage of hydatiform degeneration. The coelomic cavity of the ovum 

 was in part filled with coagulated magma, embedded in which was what 

 appeared to be a very atrophic embryo. This specimen constitutes 

 the youngest stage of hydatiform degeneration that has thus far been 

 observed, and is an excellent example of inevitable abortion, the cause 

 of which, in Dr. Williams's opinion, is to be found in a primary abnor- 

 mality of the ovum. 



Further evidence has been obtained by Dr. G. W. Corner that primary 

 abnormality of the ovum, rather than faulty implantation, is in many 

 cases the cause of pathological embryos. Dr. Corner has perfected the 

 technique of removing early blastodermic vesicles before their attach- 

 ment to the uterine mucosa (pig), and among them he has frequently 

 found specimens under 2 weeks of age which show degenerative 

 changes and abnormalities of growth. 



Dr. Corner has also described a rare case of true bilateral hermaphro- 

 ditism, with a functional ovary on one side and a testis on the other. 

 The specimen was obtained from a pig. The uterus has two normally 

 formed cornua, one of which ended in a normal Fallopian tube in con- 



