94 CARNEGIE INSTITUTION OF WA.SHINGTON. 



the brain of rats by inserting a hot needle into the cerebrum. At 

 varying intervals the animals were injected intraperitoneally with 

 trypan blue, which rendered the macrophages plainly visible. Stages 

 of repair were studied ranging from immediately after the injury to 

 the seventy-fourth day. Other experiments were made in which a 

 cold needle was used, and in some cases a hole was cut in the brain 

 and bits of sterile muscle, liver, or spleen were inserted for the pur- 

 pose of determining the possibility of attracting thither premacro- 

 phages which might develop into macrophages of a more trypanophilic 

 type. Finally, injuries equivalent to a simple concussion and to a 

 depressed fracture were produced. The authors give a complete 

 description of the gross pathology and histopathology of the pro- 

 cesses of inflammation and repair of the brain tissue following these 

 various experimentally produced lesions, which account will be of 

 the greatest importance to the neuropathologist as well as to the 

 cytologist. 



YOUNG HUMAN EMBRYOS. 



The literature contains descriptions, accompanied by authentic 

 clinical data, of 16 very young and apparently normal human ova of 

 the presomite period. In addition there are accounts of 4 similar 

 specimens which are probably normal, but concerning which clinical 

 data are lacking. When one arranges all of these specimens in their 

 respective order of development they will be found to fall into three 

 clearly defined groups: (1) those in which the primitive groove has not 

 yet appeared; (2) those in which there is a primitive groove but no 

 neurenteric canal; (3) those in which the neurenteric canal and medul- 

 lary groove can be definitely recognized. Through the kindness of 

 Dr. Horace N. Mateer I have had an opportunity to study a well- 

 preserved, normal specimen which would belong to the second of these 

 groups and which has a probable age (fertilization) of 17 days. On 

 account of the rarity of these very young ova and the relatively good 

 condition of this particular specimen, a full description of it has been 

 published. Anyone who has had occasion to study the form of these 

 early human ova can not have failed to be impressed with the urgency 

 of more and better material of this character. Most of the specimens 

 thus far published are inadequate in one way or another for satisfactory 

 study. The desired specimens must come from the operating room, 

 and toward this end the closest cooperation should be established with 

 clinics and hospitals. 



Contained within the same chorion with the young embryo in ques- 

 tion was an apparently still smaller twin, consisting of two minute 

 epithelial vesicles which were embedded in the body stalk of its larger 

 mate. Should further material confirm this as a twin, it will have an im- 

 portant bearing upon the problem of twin formation in man, as it rep- 

 resents the youngest stage yet observed. In any event, it is probable 



