DEPARTMENT OF EMBRYOLOGY. 93 



24 hours. The type of degeneration is very characteristic. It consists 

 of the immediate formation of vacuoles within the cytoplasm of the 

 cells, presenting an appearance not unlike that seen in old cultures 

 which have not been inoculated. The vacuoles rapidly increase in 

 size and number, to some extent coalescing, so that after a few hours 

 the cytoplasm is crowded with them. They arrange themselves around 

 an area corresponding to the centrosphere at one side of the nucleus. 

 The nucleus itself does not become vacuolated. 



Several kinds of bacteria were tested, some of which did not cause any 

 vacuohzation ; others brought about a moderate reaction, but none of 

 them caused the process to take place so rapidly or so extensively as 

 did the typhoid bacillus. In normal cultures inoculated with this or- 

 ganism, where the cells were undergoing mitosis, both the di\dding cells 

 and the resting cells became vacuolated. The mitotic process was com- 

 pleted, but very few new figures were formed. When the cultures were 

 stained with neutral red before being inoculated the vacuoles were red 

 from their very first appearance, as is the case with degenerating cells 

 in tissue cultures. As for the bacterial organisms, they could be seen 

 within the vacuoles about an hour after inoculation, increasing in 

 number and in distribution as time went on. Not all of the vacuoles, 

 however, contained bacteria, nor were any observed in the nuclei. 

 The number of cells containing bacteria was rather small, but was not 

 limited to one type, the organisms being present in connective tissue, 

 mesothelium, and endoderm. In almost every culture they remained 

 active and increased in number. 



As the vacuoles appeared almost immediately after inoculation and 

 the bacteria not until some time later, and as many of the vacuoles 

 contained none of the organisms, the process of vacuolization can not 

 be regarded as the result of ingestion of the bacteria, as has been 

 claimed by some investigators. It is of interest to note that food sub- 

 stances do not cause an increase in the number of vacuoles, although 

 some foods cause a slight increase in the number of red granules. Sub- 

 stances like phosphorus, carbon dioxide, urea, and ammonia tend to 

 cause the death of the cell, but they fail to result in such marked and 

 rapid vacuolization as follows inoculation with the typhoid bacillus. 



In connection with these cytological investigations reference should 

 be made to the work of Dr. C. C. Macklin and Dr. M. T. Mackhn, 

 who have studied brain repair in the rat by the use of tr^^an blue. 

 This is to some extent related to the investigation on bone repair 

 made by the former author and mentioned in our report of 1918. 

 The employment of vital dyes for the study of the reaction of pha- 

 gocytosis or macrophages in inflamed tissues finds a particularly 

 favorable field in the brain, since the tissue is white, contrasting well 

 with the ingested dye, and since it contains no cells which, under 

 normal conditions, take the dye. Aseptic wounds were produced in 



