578 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1910. 



III. RESULTS. 



It is not possible to give in this article a complete description of the 

 results already obtained. We will only describe the main character- 

 istics of the cultures during the different periods of their growth. 



Almost all our observations have been upon primary cultures, the 

 phases of which can be divided artificially into three periods, namely, 

 latency, growth, and death. 



1. The latent period covers the time from the inoculation of the 

 fragment in the plasmatic medium until the appearance of the first 

 cells. Note must first be taken of the appearance of the culture 

 immediately after its preparation; the fragment appears as an opaque 

 body with more or less sharply defined edges lying within a clear 

 medium. 



The length of the latent period varies according to the nature of 

 the tissues. It is very short for embryonal tissues and for malignant 

 tumors, which begin to grow 2 or 3 hours after the preparation 

 of the culture. In some cases, even, the first evidence of growth can 

 be observed after one hour and a half. The latent period of adult 

 tissues lasts generally from 24 hours to 3 or 4 days. It endured from 

 20 to 72 hours for glandular tissues like kidney, ovary, and thyroid, 

 according to the age of the animal and some other conditions. In 

 the case of a 6-day-old kitten growth began in 12 hours; in that of 

 a young dog it began after 24 to 48 hours. In the case of adult 

 animals 2 to 3 j^ears old the period extended to 48 or 72 hours. The 

 cultures of connective tissue, peritoneum and cartilage, may remain 

 without an}' evidence of growth for 3 or 4 days. 



2. The period of growth varies considerably. It is indicated by 

 the appearance, in one or several regions at the periphery of the 

 fragment, of many small points. They are the ends of the fusiform 

 cells which wander from the tissue. In the cultures of spleen the 

 original fragment is surrounded very soon by a thick crown of round 

 cells with amoeboid movements. In the cultures of Rous sarcoma 

 these cells can often be seen in less than 2 hours, but in certain cul- 

 tures of kidney of 2 or 3 year old cats the first fusiform cells appeared 

 after 4 days. It happens also that the growth begins by epithelial 

 cells, especially in the cultures of thyroid. Generally the wandering 

 and the proliferation of the cells are very active and the fragment of 

 tissue reaches the period of full growth. However, in the cultures 

 of peritoneal endothelium and of cartilage, a few cells only may be 

 seen during several days around the fragment, until the period of 

 active growth begins. The beginning of the growth can often be 

 diagnosed without a microscope by the appearance of an opaline band 

 around the tissues. The period of active growth may extend from 3 

 or 4 days to more than 25 days. The tissues like sarcoma and cer- 



